PROTECTION RELAYS

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The protection device shall provide either instantaneous or inverse time lag characteristics in the overload range and instantaneous with or without time delay in the short circuit range as specified in the Drawings and/or Bill of Quantities. The protection device shall be of the type acceptable to the Supply Authority or Licensee and JKR. The protection relays shall be of panel flush mounting type. All relays shall comply with relevant parts of IEC 60255.
Overcurrent protection shall be provided by externally connected current transformers. For overcurrent relay of IDMT (Inverse Definite Minimum Time) induction disc type, current settings shall be from 50% to 200% adjustable in 7 equal steps and time multiplier settings from 0.1 to 1.0 seconds adjustable continuously. Earth fault relay shall be attracted armature instantaneous type or IDMT induction disc type as specified. It shall have current settings from 10% to 40% adjustable in seven equal steps. The induction disc type shall have time multiplier settings ranging from 0.1 to 1.0 adjustable continuously.
Earth leakage relay (elr) shall be of the type suitable for use on a 240/415 V, 50 Hz. a.c. system and up to ambient temperature of 40 0C comply with IEC 61008-1 and 61008-2. Elr shall be provided with test button for simulation of a fault, earth leakage LED indicator and protection against nuisance tripping due to transient voltage and d.c. sensitive. Unless otherwise specified in the Drawings and/or Bill of Quantities, elr shall be of fixed sensivity instantaneous trip type.
For adjustable sensitivity and time delay type, selectivity range for sensitivity shall be 30 mA, 100 mA, 300 mA, 500 mA and 1000 mA and the time delay selectivity range of 0 s to 1 s. Elr shall incorporate with matching balanced core current transformer and shunt trip coil for the circuit breaker to which it controls the tripping shall also be provided. If specified in the Drawings and/or Bill of Quantities, the microprocessor based
protection relays shall be rated at 240V/415V and operating voltage shall be in a range from 90V to 250V. The relays shall be housed in robust panel flush mounting case to IP 54 and shall be fully tropicalised and suitable to be used up to an ambient temperature of 50 0C and relative humidity of 95%. Unless otherwise specified, the microprocessor based protection relays shall be of combined three phase over-current and earth-fault protection with definitetime and inverse-time characteristics. A 240V/120V 30VA step-down transformer shall be provided for connection from the mains to the relay.

The microprocessor based protection relays shall give numerical digital readout of set values, actual measured values and recorded values. The relays shall include a serial communication port for external connection to facilitate external reading, setting and recording of relay data and parameters by a personal computer (PC). PC connecting cable and parameter reading/setting /recording PC program shall be provided. The microprocessor based protection relays shall incorporate with built-in selfsupervision system with auto-diagnosis. The self-supervision system shall continuously monitor the relay microprocessor programs.
If a permanent fault is detected, an alarm indication shall be given. A 240V/5A alarm contact for connection to external alarm shall be provided. If current and voltage measurements are specified, the microprocessor based protection relays shall make available these measurements for local display. The measurements shall include three phase currents, three phase-to-phase voltages and three phase-to neutral voltages. The microprocessor based protection relays shall comply with relevant parts IEC 60255 and shall also comply with relevant parts of IEC 61000 on electromagnetic compatibility.

 


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