Diligent Protectors & Monitors

Diligent AC relays are available for Over Load (OL), Single Phasing (SP), Phase Reversal (PR), etc. The overload relays are available in 1ph and 3ph types. 1ph-relays are useful on single phase load and can also used as economical solution for 3 ph applications whenever load is balanced. These are classified depending on the response to the overload condition and the classification is as follows INStantaneous (INS) type. In this relay changes the state as soon as overload occurs. "Time-Delayed (DLY) type. In this the relay changes the state only after elapse of present period from the time overload occurred & stayed. "Jam (JAM) type. In this, the control relay does not respond to the overload condition for a preset time from switching on the load but after elapse of this time, the relay responds immediately to any overload. Instantaneous type is primarily made for AC loads other then motor such as: transformer, heater etc. However, it has been also used along with other logic to control motor. Time-Delayed overload relay find wide use. The tie delay provided in the relay avoids nuisance tripping in response to transient overloads but switches off the load if overload persists beyond the specified time. Most of the loads in actual practice increase temporarily and the drive is usually designed to handle this type of overloads. Jam type overload relay is quite unique and has made possible very reliable protection of loads such as Blower, Fans, Stirrer motors which was rather difficult to achieve with conventional thermal relay. Jam relay not only saves the motor, but restricts the possible damage to the equipment & loss of production by advance intimation before catastrophic failure takes place. Such situation, for example, can arise when oil-starved bearings' starts slowly seizing and if not attended in time can get heated and tear out the housing. Repair not only costs in term of money but looses precious time. Similarly, jamming of conveyor can be effectively responded by the Jam relay and catastrophic failure there of can be averted. Single Phasing (SP) protection in Diligent Protector relay is either Current Operated Single Phasing (COSP) or Voltage Operated Single Phasing (VOSP). COASP is realised by sensing each of the phase current continuously and as soon as current in any one phase is lost, control relay changes the state. This greatly limits the heavy thermal stresses due to large current flowing in the connected phase-windings of motor. VOSP protection monitor all three supply phases and acts when one of the phases of 3 phase supply is missing. However, Should phase be lost while 3 phase motor has already running, VOSP may not trip the motor because of the induced voltage in the motor winding. However, (COSP) is effective even when the phase is lost while the motor is in operation.