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Type YCGF 11 Field Failure Relay

Type YCGF 11 Field Failure Relay

YCGF relay withdrawn from case

Features l

Induction cup unit of low inertia and high speed.

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Offset mho characteristic.

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Variable offset and diameter settings.

Application Loss of field supply to a synchronous generator can be caused by a fault in the excitation circuits or by incorrect opening of the field circuit breaker. On loss of field, the machine operates as an induction generator excited by reactive power drawn from the system to which it is connected. This could result in instability of power in the system and overheating of the rotor, especially if the machine is of the cylindrical rotor type without damping windings in the pole faces.

To avoid mal-operation due to synchronising surges and transient conditions, the relay is used with a simple definite time delay relay and arranged to initiate alarm, tripping or load shedding if adverse field conditions persist longer than a safe period. When used with generators designed for line charging which can operate at rotor angles in excess of 90°, the diameter of the circle characteristic must be set small. At this setting, the impedance locus of the machine, on loss of field, can enter and leave the relay circle characteristic at intervals depending mainly on load conditions prior to the fault. To ensure correct operation in these conditions, it is necessary to use a set of timers and auxiliary relays. This arrangement is standard for turbo-alternator sets installed by many utilities.

Description The relay is basically a low inertia, high speed, four pole induction cup unit of simple construction having operating, polarising and restraining coils. The relay has circular mho characteristic with its centre on the ‘X’ axis of the RX diagram and is offset from the origin. This offset is adjustable so that undesirable operation of the relay on power swings or loss of synchronism not accompanied by loss of field, is avoided. The diameter of the circle is also adjustable to ensure positive operation during field failure. Adjustment of circle diameter is independent of the offset.

With the relay connected as shown in Figure 2, the phase to neutral impedance of the machine, in terms of ohms, is measured. If the field supply fails, the locus of the machine terminal impedance moves inside the relay characteristic and the contacts close immediately. Figure 1: Characteristics of relay type YCGF 11

Technical data Ratings l

Current: 1A or 5A at 50 Hz

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Voltage: 110V at 50 Hz

Settings Circle diameter: 25 to 250 ohms - 1A rating. 5 to 50 ohms - 5A rating. (adjustable in 5% steps) Offset

Figure 2: External connection diagram for YCGF 11 relay

2.5 to 20 ohms - 1A rating (adjustable in 2.5 ohms steps). 0.5 to 4 ohms - 5A rating (adjustable in 0.5 ohms steps). Maximum torque angle The MTA is 270° lagging within a tolerance of ±5° Burdens l

Current circuit: 1.7 - 2.8VA per phase The burden depends on the relevant ohmic setting and the magnitude and phase angle of the load current.

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Voltage circuit: 5.0 - 7.7VA

Accuracy l

Frequency error: ±5% over the range 47 to 52 Hz

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Temperature error: ±10% over the range –20°C to +50°C

Contact ratings A light duty normally open three point contact is fitted to the induction cup unit and is rated to make, break and carry for 30 s, 10W inductive or 20W resistive with maxima of 250V and 5A dc. Insulation The relay meets the requirements of IS 3231/IEC 255-5 series `C’ - 2 kV for 1 minute. CT requirements Details furnished on request.

Case 1D, vertical case suitable for flush mounting and finished twintone and tropicalised. Suitable trip isolating switch and CT shorting switches are provided on the cradle assembly/ case.

Information required with order 1. CT secondary rating 2. VT secondary rating 3. Details of definite time delay 4. Station aux. supply voltage The relays comply fully with the requirements of IS 3231 and are suitable for use in normal tropical environments.

ALSTOM Limited Pallavaram Works: 19/1, GST Road, Pallavaram, Chennai-600 043. India. Tel: 91-044-2368621 Fax: 91-044-2367276 Email: [email protected]. © 1998 ALSTOM Limited Our policy is one of continuous development. Accordingly the design of our products may change at any time. Whilst every effort is made to produce up to date literature, this brochure should only be regarded as a guide and is intended for information purposes only. Its contents do not constitute an offer for sale or advice on the application of any product referred to in it. ALSTOM Limited cannot be held responsible for any reliance on any decision taken on its contents without specific advice

PR:080:0799:A

Printed in India.