The main products

Spare parts spare parts, the DCS control system of PLC system and the robot system spare parts,

Brand advantage: Allen Bradley, BentlyNevada, ABB, Emerson Ovation, Honeywell DCS, Rockwell ICS Triplex, FOXBORO, Schneider PLC, GE Fanuc, Motorola, HIMA, TRICONEX, Prosoft etc. Various kinds of imported industrial parts

IMS MX-CS101-701-G1 Control module

An NPS current is usually caused by asymmetrical loading of the three phases, but may also be the result of an open-circuit phase (single-phasing). An asymmetrical load on a generator produces a magnetic field, which rotates in the opposite direction to the positive-sequence field. The negative-phase sequence flux induces currents in the rotor and these result in additional rotor losses and increased rotor temperature. The latter can represent a hazard for the rotor and this is the reason for the NPS protection. The asymmetry of the load on a generator is defined in terms of the negative-sequence stator current I2, which is therefore the quantity monitored. The definite time NPS function is intended for systems where asymmetries are of longer duration, but do not change frequently. This generally applies in the case of small to mediumsize generators. Two NPS stages are used, one for alarm and one for tripping. The maximum continuous NPS current rating I2 is given by the generator manufacturer usually as a percentage of the generator rated current IGN. The alarm stage is normally set to I2
or somewhat lower, e.g. for I2
= 10 % IGN, "I2-Setting" is set to 8 % IGN. The tripping stage is set to 50 to 100 % higher than the alarm stage, e.g. I2-Setting = 15 % IGN The NPS protection is always delayed to avoid false tripping during transient phenomena and especially during phase-tophase and earth faults on the power system. The delay may be relatively long, because the temperature rise of the endangered parts of the rotor is relatively slow.

Overvoltage setting (V-Setting)

 Please note that, although a setting of 2.0 UN is permitted, the measuring range of the c.t./v.t. input channels is only 1.3 UN (i.e. 130 V resp. 260 V max.). The first stage is intended for moderate overvoltages of long duration. The second stage provides protection against high overvoltages and is set to 70 % of the stator test voltage. Where the rated voltages of the protected unit and the v.t's differ, the primary pick-up value in p.u. does not agree with the setting of the protection and this has to be compensated using the reference value of the A/D channel. For example, for a generator rated voltage of UGN = 12 kV and a primary v.t. rated voltage of U1N = 15 kV, the setting of the second stage is Settings: Voltage V-Setting Delay Delay Over or undervoltage MaxMin Single or three-phase meas. NrOfPhases By detecting excessively high voltages, the overvoltage function prevents insulation breakdown of the windings of generator stators and power transformers and also excessive temperature rise due to increased iron losses. Excessively high voltages of longer duration are especially likely in the event of voltage regulator failure. A time delay is set to prevent false tripping during transients. Usually there are two voltage stages, both of which are arranged to trip the protected unit.