Consolidated Protective Relay List (RDSO Spec) — Traction Distribution Notes

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This chapter is an extract of a real, independent RDSO Specification (No. ETL/PSL/65(8/84)) — distinct from the main chapters covered earlier in this subject. It gives a clean, itemised consolidated list of protective relays, genuinely useful as a memorisation checklist since it summarises what earlier chapters covered individually in depth.

Where Relays Physically Sit

For protection of transformer, substation, and feeder, all relays are provided on a control panel housed in the MASONRY CUBICLE at the traction sub-station (TSS) — a real, specific physical detail about relay housing.

(i) Transformer Protection — The Real 5-Item List

Differential relays.
IDMT (Inverse Definite Minimum Time) over-current relays — for BOTH primary (HV) and secondary (LV) sides. The HV-side IDMT relay ALSO carries an instantaneous over-current element.
Instantaneous Earth Leakage relays — on BOTH primary (HV) and secondary (LV) sides.
High-speed Inter-Tripping relays.
Auxiliary relays for transformer faults — namely Buchholz, Excessive Winding and Oil Temperature trip/alarm, and Low Oil Level alarm.

(ii) Overhead Equipment Protection — The Real 5-Item List

Admittance-type DIRECTIONAL Distance Protection relays — the same Mho relay covered earlier, described here with the added technical term 'admittance-type' and 'directional.'
Admittance-type relay for protection against Wrong Phase Coupling.
Instantaneous Over-Current Relays.
Panto Flashover Relay.
Delta-I relay for high-resistance fault.

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Exam Focus — 'Admittance-Type' Is the Real Technical Term for Mho Relays

This RDSO specification uses 'Admittance-type Directional Distance Protection relay' as the formal technical name for what the main chapters simply call the 'Mho relay' — both names refer to the SAME device. This is exactly the kind of terminology variation across documents that a real exam might exploit, testing whether a candidate recognises both names describe one relay.

Auto-Reclosing & Inter-Tripping — Real Confirming Detail

This RDSO extract adds a specific real detail not as explicitly stated in the earlier chapter: the auto-reclosing feature helps CHECK/RESTRICT the continuance of arc specifically as a moving locomotive's pantograph passes the overlap opposite the feeding post — and this specifically protects the OHE CATENARY from consequent damage, naming the catenary specifically as what's being protected, not just 'OHE' generically.