Transformer Protection Equipment 1 CSC-326 Numerical Transformer Protection Equipment Fig.1 CSC-326 Numerical Transformer Protection Equipment Application The CSC-326 is numerical reliable high-speed protection equipment, which can be used for small, medium and large power transformers. The CSC-326 includes all necessary protection functions for transformers. It integrates instantaneous and percent differential protection, restricted earth fault protection, overflux protection, thermal overload protection, overcurrent protection and impedance protection etc, along with the entire suite of current, voltage protection functions in one easily configurable economical package. The integrated functions supply the user a high flexibility so that adjustments can easily be made to select protection functions. CSC-326A is applied to two-winding transformer, CSC-326B is applied to three-winding transformer. Typical functions and arrangement for CSC-326 series are shown in table 1. Table 1 Typical Functions and Arrangement for CSC-326 Series Equipment Type Functions and arrangement CSC-326A CSC-326B Main protection Instantaneous differential protection √ √ Inrush inhibit with 2nd harmonic Fuzzy recognition of inrush based on waveform selective selective Differential protection Overflux inhibit √ √ Restricted earth fault protection for HV √ √ Overflux (definite and inverse ) for HV √ √
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instantaneous differential protection and inrush inhibit and overflux inhibit etc.)
Restricted earth fault protection for HV and MV sides
Overflux protection for HV and MV sides
Definite time overcurrent protection for HV, MV and LV sides (with selective direction)
Distance protection for HV, MV sides (Including phase to phase distance protection and
phase to earth protection)
Neutral current protection for HV and MV sides (with selective direction)
Neutral displacement protection for HV and MV sides
Pole discordance protection for HV and MV sides
Switching onto fault protection for MV and LV sides
Overload protection for HV, MV, LV sides and LV winding inside delta
Thermal overload protection for HV side
Overcurrent blocking voltage regulation protection for HV and MV sides
Zero sequence overvoltage protection for LV side
IDMTL overcurrent protection for HV, MV and LV sides
IDMTL earth fault protection for HV, MV and LV sides
Construction
The enclosure for equipment is 19 inches in width and 4U in height according to IEC
60297-3.
The equipment is flush mounted with panel cutout.
The equipment for cabinet mounting has rear connection terminals.
The front panel of the equipment is unclosed from the top of the equipment. LCD, LEDs and
keys are mounted on the panel. There is a serial interface on the panel.
Draw-out modules for serviceability are fixed by lock component.
The modules can be combined through the bus on the rear board. Both the equipment
and the other system can be combined through the rear interfaces.
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Detail See Fig 13, it shows the flush-mounted enclosure of CSC-326 with panel cutout.
Differential protection (ANSI-87T)
Differential protection is the primary protection for transformers. The main features are
as follows:
Automatic ratio and vector group compensation
CSC-326 performs automatic ratio and phase angle compensation for all possible vector
groups. This simplifies application of the relay as all the CT could be connected in wye (Star
configuration).
Treble slope percent differential protection
Percent differential protection uses a treble-slope dual break-point operating
characteristic with magnetizing inrush and overflux inhibits integrated.
IR1
ID>
Idiff
Ires
Restraint current
Diff
eren
tial c
urre
nt
Slope 3
Slope 2
Slope 1
Trip area
block area
ID>>Fast trip area
IR2
Fig2. Differential protection characteristics for transformers
Selective inrush inhibit schemes
CSC-326 provided 2 schemes to cope with the magnetizing inrush conditions. The first
scheme is a ratio between the second harmonic and the fundamental frequency component.
The second scheme is fuzzy recognition of inrush conditions based on the waveform. The
two schemes are convenient for user to select.
Overflux inhibit
Traditional 5th harmonic based overflux inhibit is integrated with the percent differential
protection.
Instantaneous differential characteristics
An instantaneous (unrestrained) differential current protection is provided for fast
tripping on severe internal faults.
CT failure supervision and CT saturation recognition
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Restricted earth fault protection (ANSI 87TN)
The restricted earth-fault protection permits high sensitivity to single-pole faults. The
neutral current and the residual currents are compared. The typical connection examples
are shown in Fig3. and Fig4.
Zero-sequence currents are calculated on the basis of the phase currents. Ratio
compensation and CT failure recognition etc are integrated in the protection.
A
B
C
Side 1A
B
C
Side 2
CSC-326 013I&
Fig3. Restricted earth fault protection on an earthed transformer winding
A
B
C
CSC-326
A
B
C
013I&
2.AI&
2.BI&
2.CI&
3.AI&
3.BI&
3.CI&
Fig4. Typical connection for restricted earth fault protection on autotransformer
The differential and restraint quantity is fitted into the restraint characteristic (See Fig5).
A number of monitoring processes avoid unwanted operation in the event of external
short-circuits. In the case of a sensitive setting, multiple measurements ensure the
necessary reliability.
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0dI
0rI
0DI
0BI
DK0
Trip area
block area
u/f
N0
N1
N2
N3
N4
N5
N6
N7
T7 t (s)T6 T5 T4 T3 T2 T1 T0
Pick
up th
resh
old
u/f
Thermal trip stage
overexcitation trip stage
Fig5. Characteristic of restricted earth-fault protection Fig6. Inverse overflux characteristic
Overflux protection (Volt/Hertz) (ANSI-24)
The overflux protection serves for detection of an unpermissible high induction in
transformers, which leads to a thermal overloading. This may occur when starting up,
shutting down under full load, with weak systems or under isolated operation. The inverse
characteristic can be set via seven points derived from the manufacturer data (see Fig.6).In
addition, a definite-time alarm stage and a definite-time trip stage can be used.
For calculation of the voltage/frequency ratio, frequency and also the maximum of the
three phase voltages are used. The frequency range from 15Hz to 65Hz can be monitored in
this way.
Thermal overload protection (ANSI 49)
This feature provides thermal overload protection for cables and transformers within
the relay zone. Thermal protection is used to safeguard against system abnormalities rather
than faults (abnormally heavy loads, etc). The temperature of the protected object is not
measured directly. Instead, thermal overload conditions are detected by calculating the
average of the currents flowing in the 3 phase conductors. This average value is fed to the
thermal algorithms.
The average current rise above a defined overload setting for a defined operating time
T, the system will be tripped to prevent damage. The formula for thermal overload is as
follow:
−×=
22
2
)(ln
θτ
IIIT
T = Thermal trip time
I = Equivalent Thermal current
Iθ = RMS Thermal current
ζ = Thermal time constant of transformer
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Additionally, alarm will be given if:
1. The average current exceeds the thermal overload alarm level. If left at this level
the current would result in a thermal overload trip.
2. The thermal state of the system exceeds a specified percentage of the protected
object’s thermal capacity alarm.
3. The step rise in the thermal state of the system is greater than a specified
percentage of the object’s thermal capacity.
The thermal overload is usual to be allocated to the source side winding; it also can be
applied to either winding as desired.
Distance protection (ANSI21)
Both phase to phase distance protection and phase to earth distance protection are
provided in CSC-326. This fast short-circuit protection protects the transformer and is a
backup protection for the power system. Phase-to-phase distance protection has two
settable impedance stages; Phase-to-earth distance protection has one stage.
In order to avoid the maloperation of the distance protection, it is blocked when VT is fail.
The distance characteristic is a mho characteristic with offset (see Fig.7).
RZ
XZ*NZ
XZ
RZ*NZ
R
X
Fig7. Tripping characteristics of distance protection
Definite overcurrent protection (ANSI50 51 67)
This protection is a backup protection for the transformer and the power system. The
protection comprises 2 stages I>. The integrated direction function can be applied to the
overcurrent protection via binary settings.
Neutral current protection
This protection function is a backup protection for the transformer and the power
system. The protection comprises 2 stages I0>. The integrated direction function can be
applied to the neutral current protection via binary settings. The earth currents are
measured directly at the star-point CT or calculated by the three phase currents.
IDMTL Overcurrent protection (51 IDMTL)
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Both IEC and ANSI pick-up curves are provided for IDMTL Overcurrent protection. They
are selective for user.
IDMTL Earth fault protection (51N IDMTL)
Both IEC and ANSI pick-up curves are provided for IDMTL Earth fault protection. They
are selected for user.
Neutral displacement protection (59N)
This protection is often used for the transformer which the neutral is not earthed. The
protection comprises 2 stage 3U0>, including one alarm stage and one trip stage. For HV
(High Voltage ) and MV (Middle Voltage) sides of the transformer, the voltage is measured
directly at the open delta VT. For LV (Low Voltage ) side , the voltage is calculated by three
phase voltages.
Pole discordance protection
Pole discordance protection evaluates current components and the circuit-breaker
auxiliary contact. The components include negative sequence current I2> and zero
sequence current 3I0>. It can be started by external via digital input.
Switching onto fault protection
This protection is to protect the bus in MV (Middle Voltage) or LV (Low Voltage) sides
when the corresponding circuit breaker is switched into a fault bus. Switching onto fault
protection evaluates a maximum current and the circuit-breaker auxiliary contact.
Other protections
The CSC-326 also provide other auxiliary protections. Including, overload protection,
overcurrent blocking voltage regulation protection. The overload protection is to protect all sides
of windings of transformer continuous overload currents. The protection only comprises a
definite time alarm stage.
External signals
For recording and processing of external trip information there are some digital inputs.
They are provided for information from auxiliary protection device.
Fault and event recorder
In a protection unit, depending on the parameterization, the instantaneous values are
used. The maximum period of a disturbance recording depends on the memory and
sampling frequency. Within the buffer several disturbance records (up to 8) can be stored
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consecutively. The number is dependent on the parameterization and nature of the fault
event data record.
The possibility to set a pre- and post trigger time and the triggering event (disturbance
recording start with activation or trip) permits flexible adaptation to the different
requirements.
The disturbance record data can be transferred either to the substation automation
system or to a PC, and evaluated depending on the user preference.
On-load measurement
The on-load measured values generated in the unit such as current, voltage, phase
angle, differential current, restraint current,2nd harmonic current as well as 5th harmonic
current can be displayed at the LCD or by means of a PC.
Trip matrix/trip circuits
The unit is equipped with some trip matrix settings, which can be set via the operator
panel.
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Technical data
Input circuits Rated current IN Rated voltage UN
Rated frequency fN Thermal overload capability In voltage circuit, continuous In current circuit, continuous
≤ 10s 1s Power consumption
In voltage circuit at UN=110V In current circuit at IN = 1A
at IN = 5A
1 or 5A 63.5V or 110V AC 50Hz 1.2×UN AC 2×IN
10×IN 70×IN less than 0.5VA less than 1VA less than 0.5VA
DC voltage supply Rated auxiliary voltage Uaux
Permissible tolerance at rated auxiliary voltage Power consumption
at energized state at quiescent state
220V DC; 110V DC -30% to +14% max. 50W max. 30W
Pick-up tolerances under rated conditions
Current values Voltage values distance values Time values
Less than 3% of set value Less than 3% of set value Less than 3% of set value Less than 20ms
Digital inputs Digital inputs for 24V DC voltage Current consumption for each inputDigital inputs for 220V/110 DC voltage Current consumption for each input
12, can be expanded 26; 2mA5mA 12, can be expanded 26; 1mA3mA
Contacts
Potential-free trip/command contacts Switching capacity make Break Permissible current ,Continuous 0.5s Switching voltage Indication contacts Switching capacity make/break Permissible current Switching voltage
32 contacts, expandable 1250VA(AC), 150W(DC) 5A 30A 250V DC 16 1250VA(AC), 150W(DC) 5A 250V DC
Mechanical structure
Housing / dimensions Weight approx. Type of terminal Protection class
19 inches, 4U 8kg Harting module terminal & circuit terminal in special design IP20
Displays LED displays unit front 8 Standards IEC 60255 series & China standards
(GB,DL)
Insulation tests Dielectric voltage test Impulse voltage test
IEC 60255-5,2kV IEC 60255-5,5kV
Immunity tests High frequency test Electrostatic discharges
IEC 60255-22-1, add.100kHz according to CHINA standard, class III
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electromagnetic field Fast transient disturbances Power frequency magnetic field Conducted disturbance of RF, amplitude modulated
IEC 60255-22-2,class IV IEC 60255-22-3,10V/m IEC 60255-22-4, class IV(8kV) IEC 61000-4-8,class III IEC 60255-22-6,10V/m
Emission tests Class according with IEC IEC 60255-25 Climatic conditions Permissible ambient temperature
during service during storage during transport Humidity class
-10ºC~+55ºC -10ºC+40ºC -25ºC~+70ºC <75%
Mechanical stress Permissible mechanical stress during service during transport
IEC 60255-21-1,class I IEC 60255-21-2,class I
communication Front port RS-232; CSPC software for interrogation of the relays, testing etc. from a PC/Laptop
Rear Port RS-485 & 2 Ethernet ports-Communication with the substation automation system. Supports IEC 61850 & IEC 60870-5-103
Differential current ID> Inrush stabilization ratio (2nd harmonic) PU & DO Times Pickup time (At 2 times of set value ID>) Pickup time (At 1.5 times of set value ID>>) Drop-off time Drop-off ratio Tolerances Pickup characteristic Inrush Restraint Additional Delay Times Others 5th Harmonic stabilization ratio percentage of slop 1 percentage of slop 3 restrain current point 1
restrain current point 2
2~100A 0.3Ie~1.0 Ie (Ie: nominal current of the reference side ) 0.05~0.30 less than 30ms less than 20ms approx. 20ms approx. 0.7 ±5% of set value or ±0.02IN ±5% of set value ±1% of set value or 10ms 0.35 fixed 0.2 fixed 0.7 fixed 0.2Ie(Ie: nominal current of the reference side ),fixed 5 Ie fixed
Restricted earth fault protection
Setting ranges Differential current I0D> Percent restrained K0D> PU & DO Times At 2 times of set value Drop-off time Drop-off ratio Tolerance Pickup characteristic
0.3Ie~1.0 Ie(Ie: nominal current of the reference side ) 0.3~0.7 less than 30ms approx. 40ms approx. 0.7 ±5% of set value or ±0.02IN
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Additional time delay less than 30ms Overflux protection (Definite-time and inverse-time Overflux )
Setting Ranges Reference voltage UN
Ratio( >N
N
ffUU
//
):
Time Delay T Pair of Values for Characteristic of
U/f PU & DO Times At 1.2 times of set value Drop-off time I> Drop-off ratio Tolerance
Ratio( >N
N
ffUU
//
):
Time delays for definite Time delays for Inverse
40~100V 1.00~1.40 0.1s~9999.0s 1.10/1.15/1.20/1.25/1.30 /1.35/1.40 less than 40ms approx. 40ms Not less than 0.96 ±2.5% of the set value less than 40ms less than 40ms or ±3% of set value
IDMTL Overcurrent protection (according to different parameter setting , IEC AND ANSI IDMTL Curves can be got )
Setting ranges Current Time constant Themal capacity factor A Curve Character Power P Supplyment constant B Tolerance Current pickup I> Time delays Drop-off ratio I>
0.1×IN to 20×IN
0.025 to 2s 0.1 to 130 0 to 2 0 to 1 ±3% of set value or ±0.02IN not less than 40ms not less than 0.95
Distance protection (including phase to
phase distance / phase to earth distance)
Setting ranges Resistance(Rz )
Reactance(Xz ) Time delay T PU & DO Times:
Shortest tripping time At 0.7 times of set value
Drop-off time Starting element Current I2> Drop-off ratio Tolerance RZ< XZ< Time delays
IN=1A :0.5 to 125Ω; IN=5A :0.1 to 25Ω; IN=1A :0.5 to 125Ω; IN=5A :0.1 to 25Ω; 0.1 to 20s approx. 0.1s less than 40ms approx.40ms 0.2IN 1.05 ±3% of set value or ±0.1Ω not more than 40ms
Definite-time overcurrent protection (with selective direction )
Setting ranges Current I> Time delay T The sensitive angle of directional element PU & DO Times At 1.2 times of set value Drop-off time I>
0.1×IN to 20×IN
0.1 to 20s -45° less than 40ms approx. 40ms
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Tolerance Current pickup I> Angle of the directional element Time delays Drop-off ratio
I>, Directional element:
Voltage threshold Angle of the directional element
±3% of set value or ±0.02IN ±2° not more than 40ms not more than 0.90 1V 170°±2°
Neutral current protection (with selective direction)
Setting ranges Current 3I0> Time delay T PU & DO Times At 1.2 times of set value Drop-off time 3I0> Tolerance Current pickup 3I0> Angle of the directional element Time delaysDrop-off ratio
3I0> Directional element: Zero voltage threshold Angle of the directional element
0.1×IN to 20×IN
0.1 to 20s less than 40ms approx. 40ms ±3% of set value or ±0.02IN ±2° not more than 40ms approx. 0.9 0.5V 160°±2°
IDMTL Earth fault(neutral current) protection(according to different parameter setting , IEC AND ANSI IDMTL Curves can be got )
Setting ranges Current 3I0> Time constant Themal capacity factor A Curve Character Power P Supplyment constant B Tolerance Current pickup 3I0> Time delays Drop-off ratio 3I0>
0.1×IN to 20×IN
0.025 to 2s 0.1 to 130 0 to 2 0 to 1 ±3% of set value or ±0.02IN not less than 40ms not less than 0.95
Neutral dispalcement protection (for HV and MV side of the transformer)
Setting ranges Voltage 3U0> Time delay T PU & DO Times At 1.2 times of set value Drop-off time 3U0> Tolerance Voltage pickup 3U0> Time delaysDrop-off ratio 3U0>
160 to 300V 0.1 to 20s less than 40ms approx. 40ms ±5% of set value or ±0.1V not more than 40ms approx. 0.9
Pole discordance protection
Setting ranges Current 3I0> Current I2> Time delay T PU & DO Times At 1.2 times of set value Drop-off time 3I0>, I2> Tolerance Current pickup 3I0>, I2> Time delays
0.1×IN to 20×IN
0.1×IN to 20×IN
0.1 to 20s less than 40ms approx. 40ms ±3% of set value or ±0.02IN not more than 40ms
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Drop-off ratio 3I0>, I2>
approx. 0.9
Switching onto fault protection
Setting ranges Current I> Time delay T PU & DO Times At 1.2 times of set value Drop-off time I> Tolerance Current pickup I> Time delaysDrop-off ratio
I>
0.1×IN to 20×IN
0.1 to 20s less than 40ms approx. 40ms ±3% of set value or ±0.02IN not more than 40ms approx. 0.9
Thermal overload protection
Setting ranges Current I> Thermal time constant
Reset ratio Tolerance Current I> Time delays
0.1×IN to 20×IN
1 to 1000mins not less than 0.95 ±3% of set value or ±0.02IN approx. 40ms
Other protection ( Overload protection; overcurrent blocking voltage regulation protection)
Setting ranges Current I> Delay times T
Reset ratio Tolerance Current I> Time delays
0.1×IN to 20×IN
0.1 to 20s not less than 0.90 ±3% of set value or ±0.02IN approx. 40ms
On-load measurement
Display of values for current for voltage for differential current for 2nd harmonic differential current for 5th harmonic differential current for power supply