GE P24DM Technical Manual

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5 NEGATIVE SEQUENCE OVERVOLTAGE PROTECTIONWhere an incoming feeder is supplying rotating plant equipment such as an induction motor, correct phasing andbalance of the supply is essential. Incorrect phase rotation will result in connected motors rotating in the wrongdirection. For directionally sensitive applications, such as elevators and conveyor belts, it is unacceptable to allowthis to happen.Imbalances on the incoming supply cause negative phase sequence voltage components. In the event of incorrectphase rotation, the supply voltage would effectively consist of 100% negative phase sequence voltage only.5.1 NEGATIVE SEQUENCE OVERVOLTAGE IMPLEMENTATIONNegative Sequence Overvoltage Protection is implemented in the NEG SEQUENCE O/V column of the relevantsettings group.The device includes one Negative Phase Sequence Overvoltage element with two stages. Only Definite time ispossible.This element monitors the input voltage rotation and magnitude (normally from a bus connected voltagetransformer) and may be interlocked with the motor contactor or circuit breaker to prevent the motor from beingenergised whilst incorrect phase rotation exists.The element is enabled using the V2>1 status and V2>2 status cells.5.2 NEGATIVE SEQUENCE OVERVOLTAGE LOGICV2>1 Voltage Set V2>1 TripV00818V2>1 StartV2>1 AccelerateVTS Fast BlockStartCounter DT&&V2Note: This diagram does not show all stages . Other stages follow similar principles.VTS Fast Block only applies for directional models .Figure 103: Negative Sequence Overvoltage logicThe Negative Voltage Sequence Overvoltage module detects when the voltage magnitude exceeds a setthreshold. When this happens, the comparator output Overvoltage Module produces a Start signal (e.g. for stage1: V2>1 Start), which signifies the "Start of protection". This can be blocked by a VTS Fast block signal. This Startsignal is applied to the DT timer module. The output of the DT timer module is the trip signal which is used to drivethe tripping output relay.The V2>1 Accelerate signal accelerates the operating time of the function, by reducing the number of confirmationcycles needed to start the function. At 50 Hz, this means the protection Start is reduced by 20 ms.5.3 APPLICATION NOTES5.3.1 SETTING GUIDELINESThe primary concern is usually the detection of incorrect phase rotation (rather than small imbalances), therefore asensitive setting is not required. The setting must be higher than any standing NPS voltage, which may be presentdue to imbalances in the measuring VT, device tolerances etc.A setting of approximately 15% of rated voltage may be typical.Chapter 10 - Voltage Protection Functions P24xM214 P24xM-TM-EN-2.1