electric motor 9

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’semployees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,or disclosed to third parties, or otherwise used in whole, or in part,without the written permission of the Vice President, EngineeringServices, Saudi Aramco.

Chapter : Electrical For additional information on this subject, contactFile Reference: EEX21609 W.A. Roussel on 874-1320

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Selecting Medium Voltage Motor Starters

Engineering Encyclopedia Electrical


Saudi Aramco DeskTop Standards

CONTENTS PAGE

SELECTING CLASS E2 COMBINATION MOTOR STARTERS(CONTROLLERS) ...................................................................................................1

Characteristics of Class E2 Combination Motor Starters (Controllers) ......1

Starter Components.........................................................................2

Electrical Ratings ............................................................................4

Motor Data .................................................................................................7

Full-Load Amperes .........................................................................7

Voltage............................................................................................7

Horsepower.....................................................................................7

Power Factor ...................................................................................8

Service Factor .................................................................................8

Fault Duties ................................................................................................8

Symmetrical Current .......................................................................9

Asymmetrical Current.....................................................................9

SELECTING POWER CIRCUIT BREAKER STARTERS ................................10

Breaker Components ................................................................................10

Circuit Breaker Compartments .....................................................10

Control Circuit ..............................................................................15

Protection Components.................................................................16

Electrical Ratings......................................................................................20

Nominal Ratings ...........................................................................20

Maximum Voltage (Column 4).....................................................20

Voltage Range Factor (K) (Column 5)..........................................21

Maximum Voltage Divided by K (Column 6) ..............................22

Continuous Current (Column 7) ...................................................22

Permissible Tripping Delay (Column 8) .......................................22

Short Circuit Current At Maximum kV (Column 9).....................23

Symmetrical Interrupting Capability (Column 10) .......................23




Closing and Latching Capability (Column 12) .............................23

SELECTING PROTECTIVE RELAYS...............................................................25

Voltage and Horsepower Ratings .............................................................25

4 kV or Greater, Less Than 10,000 hp..........................................25

4 kV or Greater, 10,000 hp or Greater ..........................................25

Types of Protective Devices.....................................................................26

Class E2 Combination Controller .................................................26

Power Circuit Breakers .................................................................27

SAES-P-114 (25 APR 94)........................................................................29

Induction Motors, 600 V or Greater, Less than 5,000 hp .............29

Induction Motors, 600 V or Greater, 5,000 hp or Greater ............29

WORK AID 1: RESOURCES USED TO SELECT A CLASS E2COMBINATION MOTOR STARTER (CONTROLLER) ..................................30

Work Aid 1A: 16-SAMSS-506 ................................................................30

Work Aid 1B: Vendor’s Literature, Westinghouse DB-8850, AMPGARDMedium Voltage Starters..........................................................................30

Work Aid 1C: NEMA ICS 2-324, Table 2-324-1 and Table 2-324-2B ...30

Work Aid 1D: Applicable Selection Procedures ......................................33

WORK AID 2: RESOURCES USED TO SELECT A POWERCIRCUIT BREAKER MOTOR STARTER........................................................34

Work Aid 2A: ANSI/IEEE Standard C37.06-1987 ..................................34

Work Aid 2B: SAES-P-114, Chapter 6 ....................................................35

Work Aid 2C: Vendor’s Literature, Westinghouse SA-11671, Medium VoltageVacClad-W Metal-Clad Switchgear .........................................................35


WORK AID 3: RESOURCES USED TO SELECT PROTECTIVERELAYS..............................................................................................................37

Work Aid 3A: ANSI/IEEE Standard C37.96-1988 ..................................37

Work Aid 3B: 16-SAMSS-506 ................................................................43




Work Aid 3C: SAES-P-114, Chapter 6 ....................................................43


GLOSSARY ........................................................................................................44

TABLE OF FIGURES

Figure 1. Class E2 Ampgard Controller................................................................1

Figure 2. Typical Control Circuit Schematic ........................................................3

Figure 3. Class E2 Controller Ratings...................................................................4

Figure 4. Class E2 Controller Voltage And Interrupting Ratings .........................5

Figure 5. Class E2 Horsepower Ratings................................................................6

Figure 6. Fault Profiles .........................................................................................9

Figure 7. Vacuum Breaker Compartments..........................................................11

Figure 8. Air-Magnetic Breaker Compartments..................................................12

Figure 9. Breaker With Open Shutters................................................................14

Figure 10. Power Circuit Breaker Control Circuit ..............................................15

Figure 11. Protection Components......................................................................16

Figure 12. Bar-Type Ct .......................................................................................17

Figure 13. Voltage Transformer..........................................................................18

Figure 14. Breaker Capability Curves.................................................................21

Figure 15. Breaker Operating Times...................................................................22

Figure 16. Medium Voltage Circuit Breaker Ratings .........................................24

Figure 17. Class E2 Controller Protection (1500 Hp Or Less)............................26

Figure 18. Power Circuit Breaker Protection (Less Than 10,000 Hp) ................27

Figure 19. Additional Protection (Greater Than 5000 Hp) .................................28

Figure 20. Backup Electromechanical Protection ...............................................28

Figure 25. Class E2 Controller Motor Current Ratings.......................................31

Figure 26. Class E2 Controller Voltage And Interrupting Ratings .....................32

Figure 27. Power Circuit Breaker Ratings ..........................................................34

Figure 28. C37.96 Mv Motor Class E2 Controller Protection Scheme...............37

Figure 29. C37.96 Class E2 Controller Protective Relays ..................................38




Figure 30. C37.96 Small Mv Motor Protection Scheme.....................................39

Figure 31. C37.96 Large Mv Motor Protection Scheme.....................................40

Figure 32a. C37.96 Power Circuit Breaker Ratings And Relay Types ...............41

Figure 32b. C37.96 Power Circuit Breaker Relay Types (Cont’d) .....................42



Saudi Aramco DeskTop Standards 1

SELECTING CLASS E2 COMBINATION MOTOR STARTERS (CONTROLLERS)

Characteristics of Class E2 Combination Motor Starters (Controllers)

A Class E2 combination starter (controller) consists of the following components: Note:Starter and controller are used interchangeably throughout this Information Sheet; bothterms are correct.

• contactor (fixed or drawout)

• isolation device, feature, or mechanism

• current limiting fuses (NEMA Type R)

• control circuit

• protective relays

Figure 1 describes a Cutler-Hammer/Westinghouse Ampgard motor starter that uses a switchas the isolation device and a drawout type contactor.

Figure 1. Class E2 Ampgard Controller




Starter Components

Contactor - Class E2 controllers use the contactor as the device that actually starts and stopsthe motor. The contactor may or may not be a drawout device. The incoming power issupplied through the fuses to the contactor. The contactor shown in Figure 1 is designed to bea drawout device that allows for easy servicing and maintenance. Interlocks are available toprevent the removal or installation of the contactor when it is closed.

Isolation Switch - The purpose of the isolation switch shown in Figure 1 is to allow the user toisolate the contactor from the main power. On some controller designs isolation isaccomplished by withdrawal of the contactor. The isolation switch is interlocked to the doorto prevent access to the contactor or other energized devices while the switch is closed. If theuser has access to the contactor while the contactor is energized, a hazardous condition exists.The isolation switch has the capability of allowing the switch to be locked out when theswitch is in the open position.

Current Limiting Fuses are used to interrupt short circuits or faults exceeding the contactor’srating.

Control Circuit - A control power transformer (CPT) supplies control power to the controlcircuit. Figure 2 shows the Ampgard motor starter control circuit diagram. Note: The controlcircuit is a vendor specified function. The control circuit for a medium voltage motor starteris similar to the control circuit of a larger low voltage combination starter. Two maindifferences do exist.

• On a medium voltage starter, the primary of the CPT is protected by smallcurrent limiting fuses.

• There is the capability to use an external source of control power for testingand maintenance purposes. An external source of control power must be usedwhen the isolation switch is open. There is no test position for the drawoutcontactor as there is for a circuit breaker.

Protective Relays are used to provide thermal overload and locked rotor protection, phase andground fault protection, and other abnormal operating conditions (e.g. single-phasing)protection. Note: Work Aid 1 was developed to assist in the selection of the controllerwithout protective relays. Work Aid 3 will describe procedures for selecting the relays.




Figure 2. Typical Control Circuit Schematic




Electrical Ratings

Electrical ratings for Class E2 controllers are specified in NEMA Standard ICS 2-324. Thespecific ratings to be discussed in this Information Sheet are maximum voltage, maximumhorsepower, contactor current rating, starter interrupting capacity and contactor interruptingcapacity. Figure 3 lists the ratings of a typical medium voltage Class E2 controller.

Figure 3. Class E2 Controller Ratings

Maximum Voltage ratings as listed in NEMA Standard ICS 2-324 are a motor utilization RMSvoltage at which the interrupting rating applies (See Figure 4).

Starter Interrupting Capacity also is listed in Figure 4. The starter’s interrupting capacity aslisted is the interrupting rating of the NEMA R current limiting fuses. Note: The three-phaseMVA rating equals 1.732 times the symmetrical amperes times the normal utilization voltage.For example: MVA = 1.732 X 50 kA X 4.6 kV 400 MVA.




Figure 4. Class E2 Controller Voltage and Interrupting Ratings




Maximum Horsepower ratings as listed in NEMA Standard ICS 2-324 (Figure 5) are shownonly for reference. The vendor must state the maximum horsepower rating for theircontrollers. Although larger horsepower rated controllers are available, SAES-P-114 limitsuse of controllers to 1500 hp (1125 kW) or less.

Contactor Current Ratings are also as listed in Figure 5. Service limit values are 1.15 times thecontinuous current ratings.

Figure 5. Class E2 Horsepower Ratings

Contactor Interrupting Capacity is the rating where the contactor must be capable of making andbreaking the maximum current at which the overload relays alone cause interruption (cross-over point). The cross-over point is determined from the characteristic curves of the overloadrelays and the total clearing time curves of the medium voltage motor circuit fuses. For thecontactor that was described in Figure 3, the contactor’s interrupting capacity is 50 MVA or7217 amperes at 4.0 kV (I = 50000/(1.732 X 4.0) = 7217A).




Motor Data

The following listed motor data should be provided to the controller vendor in order to ensureboth full utilization and proper protection of the motor.

• full-load amperes (FLA)

• voltage (kV)

• horsepower (hp)

• power factor (p.f.)

• service factor (S.F.)

Full-Load Amperes

The controller’s continuous current rating as was listed in Figure 5 is based on the nameplatefull-load amperes (FLA) of the motor. The service-limit current ratings (also listed in Figure5) represent the maximum RMS current that the controller may be expected to carry forprotracted periods in normal service. The ultimate trip rating of the overcurrent relays(Device 49) should not exceed the service-limit rating of the controller.

Voltage

The controller’s voltage rating is based on the motor’s nameplate voltage rating, which is autilization voltage and not the system nominal voltage. As was discussed in EEX215.02, a2.4 kV or 4.16 kV nominal system voltage would require 2.3 or 4.0 kV nameplate (utilization)rated motors respectively. Note: 16-SAMSS-506 requires a minimum 4.8 kV rating for ClassE2 controllers.

Horsepower

The motor’s nameplate horsepower rating is also compared to the controller’s horsepowerrating, but it is used for reference purposes only. The vendor ultimately determines themaximum horsepower rating for the specific controller at a maximum voltage. For example,the controller described in Figure 3 had a maximum horsepower rating of 2500 hp at 5 kVand 80 percent power factor.




Power Factor

Because this Module is restricted to selecting starters for induction motors, the power factor isassumed to be 80 percent. As was described in Figure 3, a synchronous motor having apower factor of 100 percent would increase the controller’s horsepower rating to 3000 hpversus 2500 hp for an 80 percent power factor motor.

Service Factor

The nameplate service factor of the motor ultimately determines the continuous current ratingof the controller because the service factor determines the nameplate full-load amperes. Note:Saudi Aramco specifies only 1.0 S.F. motors.

Fault Duties

The Class E2 controller must be capable of interrupting the maximum available fault currentat the line side terminals of controller. Per NEMA ICS 2-324, all controllers must be capableof interrupting 40 kA or 50 kA, which translates to 280 MVA or 350 MVA respectively at 4.0kV, whereas 16-SAMSS-506 requires a minimum of 350 MVA at 4.8 kV. Figure 6 describesthe voltage and current relationships under fault conditions.




Figure 6. Fault Profiles

Symmetrical Current

Virtually all electrical equipment manufactured in the United States is rated symmetrically;controllers are no exception.

Asymmetrical Current

Although most electrical equipment is rated symmetrically, it also has an impliedasymmetrical rating as well. The controller’s asymmetrical rating is 1.6 times its symmetricalrating. Note: The interrupting rating of the controller is in fact the interrupting rating of theNEMA R fuses. The ratings listed in Figure 4 are in reality the ratings of NEMA R currentlimiting fuses as governed by ANSI/IEEE Standard C37.46.




SELECTING POWER CIRCUIT BREAKER STARTERS

Power circuit breakers are typically used for controlling (starting and stopping) motors ratedgreater than 6.6 kV or greater than 8000 hp. Based on current technologies, manufacturingcontactors greater than these ratings would be cost-prohibitive. Note: SAES-P-114 requirespower circuit breaker motor starters for all motors greater than 4.0 kV and 1125 kW (1500hp). Work Aid 2 has been developed to assist in the selection of power circuit breakers.

Breaker Components

Circuit Breaker Compartments

Medium voltage circuit breakers are actually sub-components of metal-clad switchgear, andthey are constructed/manufactured in accordance with ANSI/IEEE Standard C37.06. Thefollowing conditions must exist for classification as switchgear:

• The interrupting or switching device (usually a circuit breaker) is removable,and it can be moved into a disconnected, connected test, or withdrawnpositions.

• The primary bus conductors and connections are insulated.

• Automatic shutters close off and prevent exposure of the primary circuitelements when the switching or interrupting device is removed from theoperating position.

• Both the secondary and primary contacts are self-aligning and self coupling.

• Mechanical interlocks ensure safe and proper operation.

• Grounded metal barriers enclose the major parts of the primary circuit. Theseparts include the buses, voltage transformers, control power transformers, andthe switching and interrupting devices.

• There are NO intentional spaces or openings between compartments. Noopenings help prevent a fire resulting from a switchgear failure or an electricalfault from entering other compartments or sections.




Air or Vacuum Compartments - Each vertical section is divided into four compartments by steelbarriers. Figure 7 shows the four compartments in a typical vertical section of vacuumswitchgear. The breakers and the auxiliary equipment are mounted inside and at the front ofthe vertical section. Sometimes the breakers and auxiliary compartments are combined intoone compartment as shown in Figure 7 (vacuum only).

Figure 7. Vacuum Breaker Compartments




At other times, they are located in two separate compartments with the auxiliary compartmentabove the breaker compartment as shown in Figure 8 (air breaker). Directly behind these twofront compartments is the bus compartment. The compartment in the very back of eachsection is called the cable compartment.

Figure 8. Air-Magnetic Breaker Compartments




Auxiliary Compartments - The auxiliary compartment contains many combinations ofcomponents. Typical items found in the auxiliary compartments are:

• control switches for breaker control

• metering switches for voltmeter and ammeters

• terminal blocks for control and metering

• control power fuse blocks or control power circuit breakers

• protective relays

• auxiliary control relays

• drawout voltage transformers (VTs)

• control power transformers (CPTs)

Breaker Compartments - The breaker compartment encloses the switching or interruptingdevice. The area where the circuit breaker is installed is called a cubicle, and the circuitbreaker itself is called the element. Accessing the breaker compartment is through a hingeddoor. Figure 9 shows the interior of a typical breaker compartment with the circuit breakerremoved. It also shows where the current transformers are mounted. The currenttransformers are wired to the auxiliary compartment, and they are connected to meters andprotective relays.

The main power studs or primary contacts connect the high voltage to the drawout circuitbreaker. When the breaker is removed to the test position, the shutter automatically closes toprevent unintentional connection to the high voltage power studs. Figure 9 shows the shutteropen to expose the current transformers and the main power studs. The racking or levering-inmechanism is a crank and screw mechanism that moves the breaker in and out of the cubicleand into the different positions.

The secondary contact assembly is a self-aligning assembly that connects the control circuitsbetween the drawout circuit breaker and the cubicle. The circuit breaker needs control powerto operate the tripping and closing mechanism and coils. The circuit breaker also providesnormally open and normally closed contacts from an auxiliary switch. These contacts arethen used for indicating lights on the switchgear, or they may connect into other controlcircuits.




Figure 9. Breaker With Open Shutters




Control Circuit

Control circuits (logic) were discussed in detail in EEX216.03. Figure 10 is a typical controlcircuit for a medium voltage power circuit breaker, with a DC close coil, a DC trip coil, and aDC spring charging motor.

Figure 10. Power Circuit Breaker Control Circuit




Protection Components

The protection components consists of four sub-components (Figure 11):

• instrument transformers (CTs and VTs)

• circuit breaker

• DC station battery

• relays

Failure of any of the components usually results in failure of the entire system.

Figure 11. Protection Components

Current Transformers (CTs) connect in series with the line to transform the motor line current tothe standard five amperes that are suitable for a relay or meter. Many power systemprotection schemes fail, not because of fault relays, but because the relay engineer failed totake into account the effects of CT performance (saturation). CTs can be installed as shownin Figure 9, or a separate bar-type CT can be installed, as shown in Figure 12.




Figure 12. Bar-Type CT




Voltage Transformers (VTs) are also used for protection and metering purposes. They are anintegral part of the switchgear. The VT compartment is designed so that when opened thetransformers disconnect from the high voltage. Current limiting fuses electrically protect theVTs. Figure 13 shows a typical VT drawer in the withdrawn position.

Figure 13. Voltage Transformer

DC Station Batteries when properly maintained offer the most reliable tripping source. Theyrequire no auxiliary tripping devices, and they use single-contact relays that directly energizea single trip coil in the breaker. Power circuit voltage and current conditions during time offaults do not affect a battery-trip supply; therefore, battery trip is considered the best sourcefor circuit breaker tripping. Saudi Aramco requires 125 VDC tripping power (batteries).




Relays are defined by IEEE Standard 100-1984 as devices whose function is to detectdefective lines or apparatus or other power system conditions of an abnormal or dangerousnature and to initiate appropriate control circuit action. Relays are classified as follows:

• Protective relays detect defective lines, defective apparatus, or other dangerousor intolerable conditions. These relays can either initiate or permit switching,or they can simply provide an alarm.

• Monitoring relays verify conditions on the power system or in the protectionsystem. These relays include fault detectors, alarm units, channel-monitoringrelays, synchronism verification, and network phasing. Power systemconditions that do not involve opening circuit breakers during faults can bemonitored by verification relays.

• Programming relays establish or detect electrical sequences. Programmingrelays are used for reclosing and synchronizing.

• Regulating relays are activated when an operating parameter deviates frompredetermined limits. Regulating relays function through supplementaryequipment to restore the quantity to the prescribed limits.

• Auxiliary relays operate in response to the opening or closing of the operatingcircuit to supplement another relay or device. These include timers, contact-multiplier relays, seal-in units, receiver relays, lock-out relays, closing relays,and trip relays.

Virtually all of the types of relays classified above are used to protect motors. The nextInformation Sheet will present procedures for selecting relays.




Electrical Ratings

Ratings for both the air-magnetic and the vacuum circuit breakers are identical, therefore, thefollowing information applies to both types of breakers. The best method to explain theratings of medium voltage circuit breakers is to review a typical manufacturers’ rating chart(See Figure 16). Each of these columns has a specific rating for a selected breaker. Fiverating limits never to be exceeded are:

• Rated Maximum Voltage (Column 4)

• Rated Continuous Current (Column 7)

• Rated Short Circuit Current (Column 9)

• Maximum Symmetrical Interrupting Capability (Column 10)

• Closing and Latching (Momentary) Capability (Column 11)

Nominal Ratings

Voltage Class (Column 2) - This rating is the nominal voltage rating of the breaker. This voltageshould correspond to the voltage of the system to which the breaker is to be applied. Often,you will find a 4.16 kV breaker being used in a 2.4 kV system. This situation is often true inmost new installations. Note: Even if used on a 2.4 kV system, Columns 7, 10 and 11 cannotbe exceeded.

MVA Class (Column 3) - This rating is the nominal MVA rating of the breaker, and it is used forinformation purposes only.

Maximum Voltage (Column 4)

This rating is the highest rms voltage at the rated frequency for which the breaker is designed.The three standard maximum voltages are 4.76 kV, 8.25 kV and 15 kV.




Voltage Range Factor (K) (Column 5)

The K factor is the ratio of rated maximum voltage (Column 4) to the lower limit of the rangeof operating voltage (Column 6), where the required symmetrical and asymmetricalinterrupting capabilities vary in inverse proportion to the operating voltage. The K factor isspecified by ANSI C37.06 standards. Figure 14 shows typical capability curves for a 4160volt, 250 MVA or a 13.8 kV, 500 MVA rated circuit breakers. Between the maximumvoltage of 4.76 kV (15 kV) and 3.85 kV (11.5 kV), the rated interrupting current is inverselyproportional to the operating voltage. As the operating voltage increases, the interruptingrating decreases. At 3.85 kV (11.5 kV), the interrupting rating is 36 kA (23 kA) (Column 10).At maximum kV, the interrupting rating is 29 kA (18 kA)(Column 9).

To determine the symmetrical interrupting capability of a breaker at a voltage between themaximum and minimum voltage, use the following formula.

Isym =[ISC max (Column 9) x kVmax (Column 4)]/operating voltage

Figure 14. Breaker Capability Curves




Maximum Voltage Divided by K (Column 6)

This rating is often misunderstood to be the minimum operating voltage of the breaker. Therating (number) is used to determine the maximum symmetrical interrupting capability of thebreaker (Column 10). As stated earlier, 4.16 kV nominal rated breakers are used on 2.4 kVnominal systems because 2.4 kV rated breakers are no longer manufactured.

Continuous Current (Column 7)

The rated continuous current of a circuit breaker is the designated limit of rms current at ratedfrequency that it shall be required to carry continuously without exceeding the temperaturelimitations based on a 40OC ambient temperature. The temperature limits on which the ratingof circuit breakers are based are determined by the characteristics of the insulating materialsused and the metals that are used in the current carrying components and springs. Standardcontinuous current ratings are 1200, 2000, and 3000 amps.

Permissible Tripping Delay (Column 8)

The rated permissible tripping delay is 2 seconds for all medium voltage circuit breakers. SeeFigure 15 for the IEEE Standard C37.010 breaker operating times.

Figure 15. Breaker Operating Times




Short Circuit Current At Maximum kV (Column 9)

This rating is the maximum rms current the circuit breaker will interrupt at rated maximumvoltage (Column 4).

Symmetrical Interrupting Capability (Column 10)

This rating is the maximum rms current the circuit breaker will interrupt at the maximumvoltage divided by K. This value equals K (Column 5) times rated short circuit current(Column 9). The short-time current rating specifies the maximum capability of a circuitbreaker to withstand the effects of short circuit current flow for a standard period. Formedium voltage breakers, it is usually three seconds. This rating allows time for downstreamprotective devices that are closer to the fault to operate and isolate the circuit.

Closing and Latching Capability (Column 12)

This rating indicates the breaker’s ability to close in and withstand the mechanical andthermal stresses of the maximum short circuit current of the first half-cycle. This value isvery important because mechanical stresses are directly proportional to the square of thecurrent. A medium voltage breaker is designed so that its momentary rating is 1.6 times themaximum interrupting rating (Column 10 x 1.6). If expressed in peak amperes, themomentary rating is 2.7 times the maximum interrupting rating (Column 10 x 2.7).

Note: In AC medium voltage breakers, the predetermined X/R ratio is 15 (p.f. = 6.6%, whichimplies an A.F. (Mm) equal to 1.52). It is often erroneously implied that these breakers havean asymmetrical rating of 1.6 times the symmetrical rating.




Figure 16. Medium Voltage Circuit Breaker Ratings




SELECTING PROTECTIVE RELAYS

Voltage and Horsepower Ratings

The required types of motor controllers, protection schemes, and relays for medium voltageinduction motors were categorized by SAES-P-114 (01 Jul 91), Chapter 6. Note: Work Aid3 has been developed to provide resources (standards and procedures) to select protectiverelays for medium voltage motor protection.

4 kV or Greater, Less Than 10,000 hp

SAES-P-114 (01 Jul 91), Section 6.2.4, required:

• Controller Types: (1) Combination, Class E2, with currentlimiting fuses (1500 hp or less)or (2) Power Circuit Breaker

• Relay Protection: (1) Electromechanical Relay Setor (2) Solid State MPP and Electromechanical

Relay Set

4 kV or Greater, 10,000 hp or Greater

SAES-P-114 (01 Jul 91), Section 6.2.5, required:

• Controller Type: (1) Power Circuit Breaker

• Relay Protection: (1) Electromechanical Relay Sets 1 and 2or (2) Solid State MPP and Electromechanical

Relay Set




Types of Protective Devices

Class E2 Combination Controller

SAES-P-114 (01 Jul 94), Section 6.2.4, and 16-SAMSS-506, Section 5, required motorprotection (1500 hp or less) in accordance with Figure 17. Note: The detailed purpose ofeach device was described in EEX 216.02.

Figure 17. Class E2 Controller Protection (1500 hp or Less)




Power Circuit Breakers

Electromechanical Protection - SAES-P-114 (01 Jul 94), Section 6.2.4, required induction motorprotection (less than 10,000 hp) in accordance with Figure 18. Note: The detailed purpose ofeach protective device was described inEEX 216.02.

Figure 18. Power Circuit Breaker Protection (Less Than 10,000 hp)




SAES-P-114 (01 Jul 94), Section 6.2.4, also required additional protection for inductionmotors 5000 hp or greater in accordance with Figure 19.

Figure 19. Additional Protection (Greater Than 5000 hp)

Solid-State Protection - SAES-P-114 (01 Jul 94), Section 6.2.4, also permitted use of electronicrelays (motor protection packages-MPPs) instead of electromechanical relays. However, ifmotor protection packages were used, an electromechanical set of backup relays were alsoprovided in accordance with Figure 20.

Figure 20. Backup Electromechanical Protection




SAES-P-114 (25 APR 94)

The new SAES-P-114 now specifies solid-state motor protection packages (MPPs) for allcategories of medium voltage motors. Note: Refer to EEX 216.02 for a review of MPPs.

Induction Motors, 600 V or Greater, Less than 5,000 hp

SAES-P-114 (25 APR 94), Section 6.2.4, now requires:

• Controller Types: 1) Combination, Class E2, with current-limiting fuses (for 1,500 hp or less)

or 2) Power Circuit Breaker

• Relay Protection: 1) Multifunction Motor Protection Package plus additional relays

• Overtemperature: See Para. 6.5 for Device 38B and 49T temperature monitor requirements

Induction Motors, 600 V or Greater, 5,000 hp or Greater

SAES-P-114 (25 APR 94), Section 6.2.5, now requires:

• Controller Type: Power Circuit Breaker

• Relay Protection: Multifunction Motor Protection Package plus additional relays

• Overtemperature: See Para. 6.5 for Device 38B and 49T temperature monitor requirements

Note: For the specific relay functions specified under the new SAES-P-114, refer to Handout4.




WORK AID 1: RESOURCES USED TO SELECT A CLASS E2 COMBINATIONMOTOR STARTER (CONTROLLER)

Work Aid 1A: 16-SAMSS-506

For the content of 16-SAMSS-506, refer to Handout 5.

Work Aid 1B: Vendor’s Literature, Westinghouse DB-8850, AMPGARD Medium Voltage Starters

For the content of Westinghouse DB-8850, refer to Handout 6.

Work Aid 1C: NEMA ICS 2-324, Table 2-324-1 and Table 2-324-2B

For the content of Table 2-324-1, refer to Figure 25. For the content of Table2-324-2B, refer to Figure 26.




Figure 25 lists the motor current ratings of Class E2 controllers.

Figure 25. Class E2 Controller Motor Current Ratings




Figure 26 lists the voltage and interrupting ratings of Class E2 controllers.

Figure 26. Class E2 Controller Voltage and Interrupting Ratings




Work Aid 1D: Applicable Selection Procedures

1. Collect the following data from the motor nameplate:

horsepower (hp) -full-load amperes (FLA) -voltage (kV) -service factor (S.F.) -

Note: If motor nameplate data is not available (e.g. during the preliminary design stage),calculate the motor’s full-load amperes in accordance with the following formula:

FLA = [kVA/(1.732 x kV)] x S.F.

where:

kVA equals the design horsepower rating (1 kVA = 1 hp)kV equals nominal system line-to-line voltageS.F. = 1.0 for Saudi Aramco motors

2. Collect the maximum available symmetrical short circuit current (SCA) from the systemone-line diagram:

Available short circuit current (SCA) -

3. Calculate a required controller symmetrical interrupting rating 105 percent greater thanthe maximum SCA: Note: Saudi Aramco design practices require that all electricalequipment interrupting ratings be equal to 105 percent of SCA.

controller interrupting rating in amperes - Iint = 1.05 x SCA

controller interrupting rating in MVA - MVAint = 1.732 x Iint x kV

4. Select the next standard size contactor (catalog number) from pages 26 or 27 of WorkAid 1B (Handout 6) that equals or exceeds the FLA, kV, Iint or MVAint from paragraphs1, 2 and 3 above.

5. Verify that the selected contactor meets 16-SAMSS-506 (Work Aid 1A, Handout 5)criteria.

6. Verify that the selected contactor meets NEMA ICS 2-324 (Work Aid 1C) criteria.




WORK AID 2: RESOURCES USED TO SELECT A POWER CIRCUIT BREAKER MOTOR STARTER

Work Aid 2A: ANSI/IEEE Standard C37.06-1987

Figure 27 lists the ratings of power circuit breakers.

Figure 27. Power Circuit Breaker Ratings




Work Aid 2B: SAES-P-114, Chapter 6

For the content of SAES-P-114 (25 APR 94), Chapter 6, refer to Handout 4.

Work Aid 2C: Vendor’s Literature, Westinghouse SA-11671, Medium VoltageVacClad-W Metal-Clad Switchgear

For the content of Westinghouse SA-11671, refer to Handout 7.



horsepower (hp) -full-load amperes (FLA) -voltage (kV) -service factor (S.F.) -

Note: If motor nameplate data is not available (e.g. during the preliminary design stage),calculate the motor’s full-load amperes in accordance with the following formula:

FLA = [kVA/(1.732 x kV)] x S.F.

where:

kVA equals the design horsepower rating (1 kVA = 1 hp)kV equals nominal system line-to-line voltageS.F. = 1.0 for Saudi Aramco motors

2. Collect the maximum available symmetrical short circuit current (SCA) from thesystem one-line diagram:

Available short circuit current (SCA) -

3. Calculate a required power circuit breaker symmetrical interrupting rating 105 percentgreater than the maximum SCA:

power circuit breaker interrupting rating in amperes - Iint = 1.05 x SCA

4. Calculate a required power circuit breaker closing and latching rating 2.7 times greaterthan the symmetrical interrupting rating (Iint) from paragraph 3 above:

closing and latching capability - ICL(peak) = 2.7 x Iint




5. If the breaker’s closing and latching capability is expressed in symmetrical amperes,calculate a required power circuit breaker closing and latching rating 1.6 times greaterthan the symmetrical interrupting rating (Iint) from paragraph 3 above:

closing and latching capability - ICL(sym) = 1.6 x Iint

6. Select the next standard power circuit breaker from page 6 of Work Aid 2C (Handout7) that exceeds the FLA, kV, Iint and ICL(peak) or ICL(sym) from paragraphs 1 through 5above.

7. Verify that the selected power circuit breaker meets SAES-P-114, Chapter 6 (Work Aid2B, Handout 4), criteria.

8. Verify that the selected power circuit breaker meets ANSI/IEEE Standard C37.06-1987(Work Aid 2A) criteria.




WORK AID 3: RESOURCES USED TO SELECT PROTECTIVE RELAYS

Work Aid 3A: ANSI/IEEE Standard C37.96-1988

Figure 28 describes the C37.96 relay protection scheme for medium voltage (MV) motors thatare controlled by Class E2 controllers.

Figure 28. C37.96 MV Motor Class E2 Controller Protection Scheme




Figure 29 lists the C37.96 ratings of and types of protective devices used with Class Econtrollers. Note: SAES-P-114 specifies use of Class E2 controllers only.

Figure 29. C37.96 Class E2 Controller Protective Relays




Figure 30 describes the C37.96 protection scheme for small medium voltage (MV) motorsthat are controlled by power circuit breaker controllers.

Figure 30. C37.96 Small MV Motor Protection Scheme




Figure 31 describes the C37.96 protection scheme for large medium voltage (MV) motors thatare controlled by power circuit breaker controllers.

Figure 31. C37.96 Large MV Motor Protection Scheme




Figures 32a and 32b lists the C37.96 ratings of relays and the relay types used with powercircuit breaker controllers.

Figure 32a. C37.96 Power Circuit Breaker Ratings and Relay Types




Figure 32b. C37.96 Power Circuit Breaker Relay Types (Cont’d)




Work Aid 3B: 16-SAMSS-506

For the content of 16-SAMSS-506, refer to Handout 5.

Work Aid 3C: SAES-P-114, Chapter 6

For the content of SAES-P-114 (25 APR 94), Chapter 6, refer to Handout 4.



horsepower (hp) -voltage (kV) -

2. Select the MPP relay functions and types from the charts and accompanying notes onpages 24 through 28 of SAES-P-114 (Handout 4).

3. Verify that the selected relays meet ANSI/IEEE Standard C37.96(Work Aid 3A) criteria.

4. Verify that the selected relays meet 16-SAMSS-506 (Work Aid 3B, Handout 5)criteria.

5. Using the relay symbols and device numbers sketch and label a motor protectionscheme one-line diagram.




GLOSSARY

air-magnetic breaker A type of medium voltage circuit breaker with its contacts inair. A powerful electromagnet built into the arc chutes aids inextinguishing the arc.

American National An organization whose members approve various standardsforStandards Institute use in American industries.(ANSI)

arc chute A structure affording a confined space or passage way,usually lined with arc-resisting material, into or through whichan arc is directed to be extinguished.

asymmetrical (current) The combination of the symmetrical component and thedirect-current component of the current.

circuit breaker A mechanical switching device, capable of making, carrying,and breaking currents under normal and abnormal circuitconditions.

combination starter A complete motor starter consisting of a disconnect device, amagnetic contactor, and protective devices for short circuitand overload. All devices are assembled in a single enclosure.

contactor A magnetic device that has sufficient capability to start andstop a motor under normal and overload conditions.

current-limiting (fuse) A fuse that, when it is melted by a current within its specifiedcurrent-limiting range, abruptly introduces a high arc voltageto reduce the current magnitude and duration. Note: Thevalues specified in standards for the threshold ratio, peak let-through current, and I2t characteristic are used as themeasures of current-limiting ability.

frame size A term that denotes the maximum continuous current rating inamperes of a circuit breaker.

horsepower (shaft) (hp) The mechanical output (shaft) rating of a motor. One (1) hpequals 746 watts. See kilowatt (shaft).

induction motor An alternating-current motor in which a primary winding onone member (usually the stator) is connected to the powersource, and a polyphase secondary winding or a squirrel-cage




secondary winding on the other member (usually the rotor)carries induced current.




instantaneous (relay) A qualifying term applied to a relay indicating that no delay ispurposely introduced in its action.

Institute of Electrical A worldwide society of electrical and electronics engineers.and ElectronicsEngineers (IEEE)

kilowatt (shaft) (kw) The mechanical output (shaft) rating of a motor. Seehorsepower (hp).

locked-rotor The condition existing when the circuits of a motor areenergized(rotating machinery) but when the rotor is not turning.

locked-rotor current The steady-state current taken from the line with the rotorlocked and with rated voltage (and rated frequency in the caseof alternating-current motors) being applied to the motor.

locked-rotor indicating Code letters marked on a motor nameplate to show motorcode letter kVA per hp under locked-rotor conditions.

manual starter A starter that is operated by hand. Starting and stopping isperformed by devices that are operated manually.

maximum design The highest voltage at which the device is designed to operate.voltage

medium voltage Voltage levels greater than or equal to 1000 volts and lessthan 100,000 volts.

momentary current The current flowing in a device at the major peak of themaximum cycle as determined from the envelope of thecurrent wave.

motor control center A metal enclosure that contains several combination starters.(MCC)

motor protection A solid-state, self-contained motor protection relay such as thepackage (MPP) Multilin 269 Plus or the Westinghouse IQ-1000II.

National Electric Code An electrical safety code developed and approved every three(NEC) years by the National Fire Protection Association (NFPA).




National Electrical A nonprofit trade association of manufacturers of electricalManufacturers apparatus and supplies, whose members are engaged inAssociation (NEMA) standardization to facilitate understanding between usersand manufacturers of electrical products.

negative sequence Three balanced current phasors that are equal in magnitudethatcurrent components are displaced from each other by 1200 in phase, and that havethe phase sequence opposite to that of the original set ofunbalanced phasors.

nominal system voltage A nominal value assigned to designate a system of a givenvoltage class.

oil circuit breaker A type of circuit breaker that uses mineral oil as an insulatingand arc interrupting medium.

overload relay A device that is used to sense an overload on a motor circuit.The most common type uses a heater that heats a bi-metallicstrip that operates a set of contacts.

pilot device Control and indicating devices used in motor control circuits.These devices include indicating lights, switches andpushbuttons.

positive sequence Three balanced current phasors that are equal in magnitudethatcurrent components are displaced from each other by 1200 in phase, and that have

the same phase sequence as the original unbalanced phasors.

relay An electrically controlled, usually two-state, device that opensand closes electrical contacts to affect the operation of otherdevices in the same or another electric circuit.

replica temperature A thermal relay whose internal temperature rise isproportionalrelay over a range of values and durations of overloads to that of the

protected apparatus.

residual (current) The sum of the three-phase currents on a three-phase circuit.The current that flows in the neutral return circuit of threewye-connected current transformers is residual current.

rotor The rotating member of a machine, with shaft.(rotating machinery)




service factor A multiplier that, when applied to the rated power, indicates apermissible power loading that may be carried under theconditions specified for the service factor.

short-time rating A rating for low voltage power circuit breakers and mediumvoltage breakers that describes the breakers ability towithstand a fault current for a period of time. If a breakerdoes not have an instantaneous trip unit, it must have a short-time rating.

single-phasing (motor) An abnormal operation of a polyphase machine when itssupply is effectively single-phase.

starter (motor) An electric controller for accelerating a motor from rest tonormal speed and for stopping the motor.

starting current The current drawn by the motor during the starting(rotating machinery) period. This current is a function of speed or slip.

stator The portion that includes and supports the stationary(rotating machinery) active parts. The stator includes the stationary rtions of the

magnetic circuit and the associated winding and leads. It may,depending on the design, include a frame or shell, winding supports, ventilation circuits, coolers, and temperature

detectors. A base, if provided, is not ordinarily considered to be part of the stator.

sulphur-hexafluoride A type of circuit breaker that uses sulfur-hexafloridecircuit breaker (SF6) gas as an insulating and arc extinguishing medium.

vacuum circuit breaker A specific type of medium voltage circuit breaker that isdesigned to interrupt the arc inside a container that is under avacuum. This vacuum limits ionization of gases and makesthe circuit breaker lighter and more compact.

symmetrical (current) A periodic alternating current in which points one-half aperiod apart are equal and have opposite signs.

synchronous speed The speed of the rotation of the magnetic flux, produced by orlinking the winding.

temperature rise A test undertaken to determine the temperature rise(rotating machinery) above ambient of one or more parts of a machine underspecified operating conditions. Note: The specified conditions mayrefer to current, load, etc.




time-current The correlated values of time and current that designatecharacteristics the performance of all or a stated portion of the functions of a

protective device. Note: The time-current characteristics of a protective device are usually shown as a curve.

time-overcurrent relay An overcurrent relay in which the input current and operatingtime are inversely related throughout a substantial portion ofthe performance range.

total current See asymmetrical current.

zero sequence Three balanced current phasors equal in magnitudecurrent components and with zero displacement from each other.

electric motor 9

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