DC supply & Trip Indications of 11KV MetalClad Switchgear according to WAPDA Specification P-44:96

• Supervision relay shall be provided for continuously monitoring the healthy conditions of breaker trip circuit and presence of DC supply on all applicable panels. The presence of healthy trip circuit shall be indicated by the continuous glow of a yellow lamp. The indicating lamps shall be of neon type with screwed base. The rating shall be 5 Watt at 150V or 260V DC depending on control and auxiliary supply voltage.
• One hooter and its acknowledge and cancelling arrangement shall be installed in the incoming panel to indicate failure of DC main supply, DC supply to any panel and failure of healthy trip circuit and tripping of any breaker. This arrangement should be self contained and securely fixed to the panel. The alarm cancelling arrangement shall be flush mounted on the front of the panel.
• For circuit breaker fitted with AC series trip mechanism, auxiliary contacts shall be provided in the protective relay for operation of a hooter, installed in the incoming panel, to indicate breaker trip. The contact shall be suitable for operation for the hooter. 

Differential Protection of 11KV MetalClad Switchgear according to WAPDA Specification P-44:96

• All incoming panels shall be provided three additional CTs for differential protection.
• The differential protection zone of power transformers is required to trip the 11KV incoming breakers. For this purpose the incoming panels of 12.5KA rating shall be provided with an additional DC operated trip coil.
  

Over Current Protection of 11KV MetalClad Switchgear according to WAPDA Specification P-44:96

• All panels shall have overcurrent & earth fault protection which shall be provided by means of inverse induction type/numeric type relays with two over current elements and one earth fault element. The relays shall have three instantaneous elements.
• For 12.5KA switchgear, the relays shall be arranged to operate on AC and without any external source of supply using saturable auxiliary current transformer.

• For 25KA switchgear, the over current relays shall operate on DC.
• For 25KA Incoming Panels, in addition to the DC protection scheme, a back up AC series protection scheme shall also be provide. The back up AC series protection shall be operated by a separate earth fault relay. The characteristics of earth fault relay for back up protection shall be same as for earth fault unit in the main over current  and earth fault relay. For AC back up protection the trip coils shall be energized directly from the CTs without  requiring any external source 

Short-Circuit Strength of 11KV MetalClad Switchgear according to WAPDA Specification P-44:96

• The Switchgear, all apparatus and connections shall be so supported and proportioned as to be capable of safely withstanding stresses to which they may be subjected during service including those due to short circuit of 12.5KA or 25KA as required and under the cinematic conditions specified herein.
• Each panels shall be designed  to carry and withstand thermal and mechanical stresses caused by the following rated currents:

•   12.5 KA Panels:

1. Rated normal current  (for main-circuits)                                                400A & 1250A 
2. Rated short-time (1 sec) withstand current (for main & earthing circuits)        12.5KA
3. Rated peak withstand current (for main & earthing circuits)                                 32KA

•   25 KA Panels:

1. Rated normal current  (for main-circuits)                                                630A & 2500A 
2. Rated short-time (1 sec) withstand current (for main & earthing circuits)           25KA
3. Rated peak withstand current (for main & earthing circuits)                                 63KA