This video contains all the details of Indian Railways Relays
A-LINE OF PROTECTION IN TSS-There are 04 level of protection in TSS
a.HV side (132 kV) protection
b.Transformer Protection
c.LV Side (27 kV) protection
d.Feeder protection (OHE)
B-What is Fault MVA & importance in protection system ?
Fault MVA taken as per data provided by SEB considering three phase bus bar fault at GSS and all the impedance (loop impedance of transmission line, power transformer impedance & feeder impedance) at TSS.
Fault MVA should be taken in such a way that fault occurring in TSS should always trip TSS CB not GSS CB.
Faults in feeder line should trip first feeder CB then LV CB as back up CB
Fault in LV Bus bar should trip first LV CB then as a back up HV CB.
Fault in HV side should trip HV CB first then GSS CB.
Not in any case GSS CB should trip first, in case the fault in TSS.
Calculation of protection system relay in TSS depends on Fault MVA & Power Transformer parameters (Rating, impedance) & feeder line (OHE) impedance.
C.HV Side (132 kV) Protection
1. REF (Restricted Earth Fault)
This relay will operate during any earth fault within the restricted zone in TSS
As the pick up value is very low, setting of this relay should 10% of full load primary current of power transformer.
This is provided as a back up protection to the differential protection for internal earth faults of transformer winding in addition to earth faults in the restricted zone between the transformer breaker and the winding.
2. Over Current Relay
a) IDMT (Inverse Definite Minimum Time)
This relay will operate after the pre set value of Over load condition with time delay.
To use over load capacity of power transformer the setting of IDMT relay should be 190% of transformer full load primary current.
TMS (Time Multiplier Setting) should be in such a way that operating time of HV CB through IDMT relay should 600 ms for bus fault.
b) Instantaneous Over Current Relay- The setting of this relay should be 1.25 times of bus bar fault current in LV refer to HV side to eliminate chance of tripping in case of LV bus bar fault.
D- LV Side (27 kV) Protection
1. REF (Restricted Earth Fault)
This relay will operate during any earth fault within the restricted zone in TSS
As the pick up value is very low, setting of this relay should 10% of full load primary current of power transformer.
This is provided as a back up protection to the differential protection for internal earth faults of transformer winding in addition to earth faults in the restricted zone between the transformer breaker and the winding.
2. Over Current Relay
a) IDMT (Inverse Definite Minimum Time)
This relay will operate after the pre set value of Over load condition with time delay.
To use over load capacity of power transformer the setting of IDMT relay should be 180% of transformer full load primary current.
TMS (Time Multiplier Setting) should be in such a way that operating time of LV CB through IDMT relay should 300 ms for bus fault.
This relay act as a back up protection for feeder CB.
E- Feeder protection Relay
Distance Protection
Wrong Phase Coupling
PT fuse failure
Instantaneous Over Current Protection
Auto-re-closer
LBB Protection
Trip Circuit Supervision
Panto Flash Over Relay
Vectorial Delta-I Protection
Note: All the relays can be enabled or disabled individually
Distance Protection Relay
Distance relays differ in principle from other forms of protection in that their performance is not governed by the magnitude of the current or voltage in the protected circuit but rather on the ratio of these two quantities. Distance relays are actually double actuating quantity relays with one coil energized by voltage and other coil by current.
The current element produces a positive or pick up torque while the voltage element produces a negative or reset torque. The relay operates only when the V/I ratio falls below a predetermined value(or set value).During a fault on the transmission line the fault current increases and the voltage at the fault point decreases.
The V/I ratio is measured at the location of CTs and PTs. The voltage at the PT location depends on the distance between the PT and the fault. If the measured voltage is lesser, that means the fault is nearer and vice-versa. Hence the protection called Distance relay.