POWER DISTRIBUTION 2.docx

POWER DISTRIBUTIONTRAINING

GOALS OF TRAINING

•Electrical Distribution Equipment (Transformers, Switch Gear, Gen., Breakers)

•One-line Diagram Interpretation

•Hands-on Application

•Restoring Power

What is a Transformer?

NO YES

CHARACTERISTICS OF A TRANSFORMER

•A transformer is a static device which transforms electrical power from one voltage or current level to another keeping the same frequency through electromagnetic induction.•A varying current in the transformer's primary winding creates a varying magnetic flux at the secondary induces a varying electromotive force or voltage in the secondary winding.

High Voltage Transformers Characteristics•Steps primary voltage (28KV) down on the secondary voltage (4160V)•Oil inside of these transformers acts as a cooling agent to reduce heat

•Nitrogen is applied to transformers to remove oxygen and water

Medium Voltage Switchgear

•Combination of electrical disconnect switches, fuses or circuit breakers used to control, meter, protect and isolate electrical equipment•Has a main breaker that applies the secondary voltage (4160V) to bus lines upon closing•Has two incoming feeds separated by a tie-breaker.

Breaker Function

•The main function of a breaker is to connect/disconnect to or from a bus line upon closing/opening. •They also have a protective feature of opening or “tripping” on high currents•Although there are various types of breakers (air or vacuum) the function remains the same.

Substations & Motor Control Centers

Have a transformer to step the primary voltage (4160V) down to the secondary voltage (480V)

An assembly of one or more enclosed sections having a common power bus

Emergency Generators

•Diesel powered systems that generate their own power to be applied to switchgear automatically in the event of full power loss•Have a peak shaving component that aids in power consumption reduction

ONE-LINE DIAGRAMS

A line diagram is used to show the relationship between circuits and their components but not the actual location of the components

TYPICAL ELECTRICAL DRAWING SYMBOLS

Simple One-Line Diagram Schematic

Loss of Power Scenarios

Scenario: A plant with 2 transformers has the motor load evenly distributed. No bus ties are closed.

There is a loss of power on transformer 1. What happens?

There is a power loss on 1 and 2 transformers. What happens?

The breaker feeding one side of the substation fails open. What happens?

Controlled Shutdown

In the event of an scheduled shutdown of one or more primary transformers, what are some of the procedures that need to be followed?

1. First unload affected switchgear bus by removing pumps from service and tying substation feeds to provide for uninterrupted service as needed.

3. Remove control fuses

2. Open main breaker from control panel remote switch

Remove control fuses

4. For further isolation breaker may be lowered and removed from cabinet.

BREAKERS

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow.

The circuit breaker which operates in air at atmospheric pressure. For interrupting arc it creates an arc voltage in excess of the supply voltage.

Vacuum Circuit Breakers

These breakers interrupt the current by creating and extinguishing the arc in a vacuum container - aka "bottle". Long life bellows are designed to travel the 6-10 mm the contacts must part. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air circuit breakers

Oil Circuit Breakers

The oil is used to insulate between the phases and between the phases and the ground, and to extinguish the arc. When electric arc is drawn under oil, the arc vaporizes the oil and creates a large bubble of hydrogen that surrounds the arc. The oil surrounding the bubble conducts the heat away from the arc and thus also contributes to deionization and extinction of the arc.

Purpose of Main/Tie Breakers/Interlocks

The tie breaker system is designed only to have one transformer operating when the tie breakers are closed, or in other words the system is not intended to run with the utility transformer paralleled. Interlock systems are in place to ensure that the ties and both mains are never all closed at once putting transformers in parallel.

Typical Tie-Breaker with Interlocks

Difference Between Breakers for Medium Voltage and Substations

Substations transform voltage from high to low, typically 4160V to 480V, and operate under the same governing principles as medium voltage switchgear.

Switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment loads of 4160V

Open Transition Breaker

It prevents back feeding from an emergency generator back into the utility line

Closed Transition

synchronization : voltage difference less than 5%, frequency difference less than 0.2 Hz, and maximum phase angle between the sources of 5 electrical degrees

Raking in and out of Breakers

Racking provides a method of isolating a high-voltage metal-clad circuit breaker from its supply and load circuits, and/or to provide grounding. Before racking, the circuit breaker must be opened, and this is usually ensured using an interlock system.

RESTORING POWER

1. Knowledge of Procedure

2. Response Time

3. Contacting Effected Parties

4. Investigating the Cause

5. Waiting for Stability

Restoring Power Scenarios

There is a loss of power on transformer 1. How do you restore power?

There is a power loss on 1 and 2 transformers. How do you restore power?

The breaker feeding one side of substation 1 fails open. How do you restore power?

Southwest ProceduresIf under normal operations, either Transformer 1 or 2 has lost power:1. Look at the control board to determine which transformer has been lost.

2. Close the trip/close switch for the tie breaker so that transformer 1 powers up bus1 and bus 2 and trip the trip/close switch for transformer 2 or

3. Close the trip/close switch for the tie breaker so that transformer 2 powers up bus 1 and bus 2 and trip the trip/close switch for transformer 1(depending on which transformer has been lost).

4. If no high lift pump is in service due to the power loss, start a high lift pump as soon as possible to restore system pressure.

5. Notify systems control and the senior chemist that there has been a loss of power and request their preference as to which pumps should be put in service so that adjustments can be made.

6. Put the desired high lift and low lift pumps in service.

7. The sr. operator, operator and sr. chemist will coordinate to restart all equipment and machinery that may have been affected by the power loss.

8. Be sure to do a trouble report so that the emergency can be documented.

Response Time

It is critical to react safely, competently and quickly to power loss events. Being aware of what power source is supplying equipment in service, and relying on your team (Water Techs, Chemist, SCC) to provide information in cause of an loss is essential.

If possible, starting another pump to restore system pressure is the priority over restoring loss power.

Contacting DTE/SCC/Management

Notification of power loss and the current status is crucial during a power loss event.

Contact numbers for SCC and DTE should be posted or readily available.

Notification of management and detailed documentation of what occurred and the steps taken to restore power are also important.

Troubleshooting Power LossAfter restoring system pressure and establishing a power source, the next step is to investigate the potential causes of the power loss.

Although you are not an electrician, detailed notes of what has taken place during the event are necessary for the maintenance crew to find the cause and repair or replace any damaged equipment.

Following Proper Procedures/Waiting for Stability

Before normal power distribution operation can be restored, a high probability of stability must be known.

Helps to avoid a repeat of the power loss.

Working with DTE or the maintenance crew to establish cause will provide insight

You are the first line of defense in protecting the public.

Test Time