PDF Version. Use of the relay The overcurrent relay REJ 523 is intended for selective short-circuit protection in medium voltage distribution networks but can also be used for protection of generators, motors and transformers. Overcurrent Relay 1.0 APPLICATION The CO relay is a single phase non-directional time ac overcurrent device. Protective relay SlideShare. This cycle will repeat and eventually the motor Introduction 3.1. Overcurrent Elements The motor will catch fire if it is overloaded and overcurrent is In an over current relay or o/c relay the actuating quantity is only current.There is only one current operated element in the relay, no voltage coil etc. Aging (natural wear) 10% 6. This paper will review the mainstream methods by which 67 type directional decisions are made by protective relays. Abstract – Directional overcurrent relaying (67) refers to relaying that can use the phase relationship of voltage and current to determine direction to a fault. Overcurrent relaying is the simplest and cheapest, the most difficult to apply, and the quickest to need readjustment or even replacement The basic element in overcurent protection is the overcurrent relays. Single Phasing 15% 4. It is used to sense current lev-el above the setting and normally is used to trip a cir-cuit breaker to clear faults. Overcurrent Relay Overcurrent relays are those relays that respond to current only. are required to construct this protective relay.. (1) Overload elements Overcurrent elements Time elements (2) Open-phase elements (3) Reverse-phase elements These functions are described in more detail below. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay., increasing complexity of protection schemes and use of relays containing software. CO Circuit Opening Overcurrent Relay The overcurrent unit contacts are in the contactor switch coil circuit and when they close, the solenoid plunger moves upward to open the de-ion contacts which normally short circuit the trip coil. The relay will operate if the current passing through the operating coil are higher than the threshold current. GRD140 series relays provide four stage non-directional and directional overcurrent protection for distribution networks, and back-up protection for transmission and distribution networks. 259 Lines are protected by overcurrent-, distance-, or pilot-relaying equipment, depending on the requirements. There are a variety of concepts by which this task is done. Working Principle of Over Current Relay. Inverse overcurrent is normally associated with the overcurrent relay types, and the operation time is inversely proportional (in certain degrees) with their overcurrent ratio. Overcurrent 30% 2. Perhaps the most basic and necessary protective relay function is overcurrent: commanding a circuit breaker to trip when the line current becomes excessive. Overcurrent Relay Technical Reference Manual 3. An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. The REJ 523 is based on a microprocessor environment. The overcurrent relay can be used as overload (thermal) protection when protects the resistive loads, etc., however, for motor loads, the overcurrent relay cannot serve as overload protection Overload relays usually have a longer time setting than the overcurrent relays. Contamination 18% 3. Rotor Fault 5% 7. The GRD140 series has three models and provides the following protection schemes in all models. Bearing Failure 12% 5. Miscellaneous 7% ... relay trip, and unless the cause of the overload has been removed, the overload relay will trip again. 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