IMCIS22模块备件,DCS工控模块备件
功能469不平衡定义为负序电流与正序电流之比。当电机负载较轻时，必须降低额定值，以防止出现有害警报。如果启用，则在电流不平衡报警/跳闸延迟指定的时间段内，一旦不平衡量超过电流不平衡警报/跳闸拾取，就会发生跳闸和/或报警。如果不平衡水平超过40%，或当Iavg>25%FLA且任何一相的电流为零时，电机被视为单相，并在2秒内跳闸。如果不平衡功能被“关闭”，则单相保护被禁用。当设置电流不平衡报警/跳闸拾取水平时，请注意，1%的电压不平衡通常转化为6%的电流不平衡。因此，为了防止意外跳闸或报警，拾取水平不应设置得太低。此外，由于短期不平衡是常见的，因此应设置合理的延迟，以避免产生干扰性跳闸或警报。建议使用不平衡偏置特性来偏置由周期性短期不平衡引起的电机加热热模型（见第4–42页第4.6.4节：不平衡偏置）。异常高的不平衡水平可能由不正确的相位CT接线引起。b） 示例：电流不平衡水平的波动通常由电源电压引起。可能需要有一个锁存报警，以捕捉超出不平衡报警参数的任何此类波动。此外，建议旅行。如果电源电压通常不平衡达2%，典型电机的电流不平衡为2×6=12%。在这种情况下，将电流不平衡报警传感器设置为“15”，电流不平衡跳闸传感器设置为”20”，以防止意外跳闸；5或10秒是合理的延迟。❙ 电流不平衡❙ [输入]更多电流不平衡报警：关闭范围：关闭、锁定、未锁定分配报警继电器：报警范围：报警、报警和辅助2、报警和辅2和辅3、辅助电流元件4设定点编程4 4.7.6接地故障接地故障元件的功能如下。一旦接地电流幅值在延迟规定的时间内超过拾取电平×接地CT初级（见第4–11页第4.3.1节：电流传感），将发生跳闸和/或报警。还可以启用备用跳闸功能。如果接地故障跳闸备份为“开”，且已启动接地故障，则如果接地电流持续时间超过接地故障跳车备份延迟，则将发生第二次跳闸。第二次跳闸指定给R2或R3，R2或R3将专用于上游断路器跳闸继电器。接地故障跳闸备用延迟必须设置为比断路器清除时间更长的时间。❙ 接地故障❙ [输入]了解更多接地故障超范围过滤器：关闭范围：打开，关闭接地故障报警：关闭范围，锁定，未锁定分配报警继电器：报警范围：报警，报警和辅助2，
4 4.7.5 CURRENT UNBALANCE a) FUNCTION 469 unbalance is defined as the ratio of negative-sequence to positive-sequence current This derating is necessary to prevent nuisance alarms when a motor is lightly loaded. If enabled, a trip and/or alarm occurs once the unbalance magnitude exceeds the CURRENT UNBALANCE ALARM/TRIP PICKUP for a period of time specified by the CURRENT UNBALANCE ALARM/TRIP DELAY. If the unbalance level exceeds 40%, or when Iavg > 25% FLA and current in any one phase is zero, the motor is considered single phasing and a trip occurs within 2 seconds. Single phasing protection is disabled if the unbalance feature is turned "Off". When setting the CURRENT UNBALANCE ALARM/TRIP PICKUP level, note that a 1% voltage unbalance typically translates into a 6% current unbalance. Therefore, to prevent nuisance trips or alarms, the pickup level should not be set too low. Also, since short term unbalances are common, a reasonable delay should be set to avoid nuisance trips or alarms. The unbalance bias feature is recommended to bias the thermal model for motor heating caused by cyclic short term unbalances (see Section 4.6.4: UNBALANCE BIAS on page 4–42). Unusually high unbalance levels may be caused by incorrect phase CT wiring. b) EXAMPLE Fluctuations of current unbalance levels are typically caused by the supply voltage. It may be desirable to have a latched alarm to capture any such fluctuations that go beyond the Unbalance Alarm parameters. Also, a trip is recommended. If the supply voltage is normally unbalanced up to 2%, the current unbalance seen by a typical motor is 2 × 6 = 12%. In this case, set the CURRENT UNBALANCE ALARM PICKUP to "15" and the CURRENT UNBALANCE TRIP PICKUP to "20" to prevent nuisance tripping; 5 or 10 seconds is a reasonable delay. ❙ CURRENT UNBALANCE ❙ [ENTER] for more CURRENT UNBALANCE ALARM: Off Range: Off, Latched, Unlatched ASSIGN ALARM RELAYS: Alarm Range: Alarm, Alarm & Auxiliary2, Alarm & Aux2 & Aux3, Auxiliary CURRENT ELEMENTS 4 SETPOINT PROGRAMMING 4 4.7.6 GROUND FAULT The Ground Fault element functions as follows. Once the ground current magnitude exceeds the Pickup Level × GROUND CT PRIMARY (see Section 4.3.1: CURRENT SENSING on page 4–11) for the time specified by the delay, a trip and/or alarm will occur. There is also a backup trip feature that can be enabled. If the GROUND FAULT TRIP BACKUP is "On", and a Ground Fault trip has initiated, a second trip will occur if the ground current persists longer than the GROUND FAULT TRIP BACKUP DELAY. It is intended that this second trip be assigned to R2 or R3, which would be dedicated as an upstream breaker trip relay. The GROUND FAULT TRIP BACKUP DELAY must be set to a time longer than the breaker clearing time. ❙ GROUND FAULT ❙ [ENTER] for more GROUND FAULT OVERREACH FILTER: Off Range: On, Off GROUND FAULT ALARM: Off Range: Off, Latched, Unlatched ASSIGN ALARM RELAYS: Alarm Range: Alarm, Alarm & Auxiliary2,
