Contents
What is relay current?
A current relay is a type of electromagnetic switch used as part of the control systems for electrical equipment. This lowers the amount of current that’s allowed to move through the system. The same functionality can be provided to machines or other electrical apparatuses to prevent damage due to undercurrent.
How do you calculate pickup current?
Pick-up current = Plug Position x Rated CT Secondary Current. The plug or tapping is provided on the Relay Coil so that changing the position of Plug changes the number of turns of the relay coil as shown in figure below.
What is TMS and PMS in relay?
Plug setting multiplier is nothing but a ratio between the actual fault current in the relay operating coil to pick up current (the relay current setting). Relay pick up current= %current setting * CT ratio.
How do you calculate PSM?
PSM = Fault Current / Actual Pick up = 500/167 = 2.99 Expected operating time for relay 2 = Operating time of relay 1+ CTI = 0.15 + 0.3 = 0.45sec. Operating time of relay 2 = 0.24sec.
What are 3 types of start relays?
Several types of starting relays are used to assist in the starting of single-phase compressors. These include the current relay, potential relay, and PTC (positive temperature coefficient) relay. Each performs the same function but in a different manner.
What is a pick up current in a relay?
The pickup current is the current that passes through the coil in creation of the deflecting force. The contact will move once the deflecting force is greater than the controlling force.
Which relay operates first?
For feeder protection, there would be more than one overcurrent relay to protect different sections of the feeder. These overcurrent relays need to coordinate with each other such that the relay nearest fault operates first.
What is PSM and TMS?
defined as the ratio where, for a given PSM T is the desired relay operating time and Tm is the corresponding operating time at TMS of 1.0. TMS is also referred to as TDS (Time Dial Setting).
How to calculate CT current for a relay?
Ex: A siemens Make motor 415 V, 3 PH, 220 KW, 0.8 Power factor, FLA = 400 Amps In starter’s CT ratio = 500 / 5, Relay range = 1.5 Amps to 5 amps, which means if your line current is 500 Amps then CT output will be 5 amps then the Line current is 400 Amps, CT output will be 4 Amps, In relay, you have to set it for 4 amps for 100 % Load (Full load)
How to calculate current for thermal over load relay?
Consider CTs are placed at the output of the contactor, In this phase current will come to action, you have to calculate phase current of the same. Take the same motor data. FLA = 400 Amps, Same CT 500/5 Amps CT output for 100 % Load will be = 2.31 Amps. You have set the current limit as 2.3A in relay
How many amps are in a relay current?
In starter’s CT ratio = 500 / 5, Relay range = 1.5 Amps to 5 amps, which means if your line current is 500 Amps then CT output will be 5 amps then the Line current is 400 Amps, CT output will be 4 Amps, In relay, you have to set it for 4 amps for 100 % Load (Full load)
How to calculate the time of operation of a relay?
Changing the position of TMS setting, changes the distance between the contact of the rotating disk and the coil. In the above figure the over current relay time characteristics are shown. By using these we can calculate Actual time of operation of the relay = (Time obtained from PSM- Operating time graph) * TMS