What is extremely inverse relay?
Extremely Inverse Relay This relay is used for protecting the cable, transformer, etc. The relay can operate instantly when the pickup value of the current is more than the relay setting time. The relay provides faster operation even under the fault current. It is used for sensing the overheating of the machines.
What is very inverse time overcurrent relay?
Very Inverse Time Overcurrent Relay. Gives more inverse characteristics than that of IDMT. Used where there is a reduction in fault current, as the distance from source increases. Particularly effective with ground faults because of their steep characteristics.
Which is the correct expression for IEC extremely inverse over current relay characteristics?
The equation describing the Extremely Inverse Relay is I2t = K where I is operating current and t is time of operation of the Relay. IEC (International Electrotechnical Commission) Standard Curve for Inverse Relays: As per IEC, the time of operation of any Inverse relay can be calculated from the formula given below.
How do you calculate TMS?
(2) TMS <= Minimum Fault Current / CT Primary Current. For Condition (1) 0.8 > =(480/600) = 0.8 >= 0.8, Which found OK. For Condition (2) 0.125 <= 11000/600 = 0.125 <= 18.33, Which found OK. Here Condition (1) and (2) are satisfied so.
What is inverse time current?
Inverse Time Over Current is also referred to as Time Over Current (TOC), or Inverse Definite Minimum Time (IDMT) which indicates that the trip time of the relay is inversely proportional to the applied fault current.
What is Idmt and DMT relay?
Generally, the over current relays are differentiating with their time of operation. The most commonly used over current relays are IDMT (Inverse definite mean time) over current relays, DT (definite time) over current relays and Instantaneous time over current relays. They are designed to sense the over-current.
What inverse current?
[′in‚vərs ′kə·rənt] (electronics) The current resulting from an inverse voltage in a contact rectifier.
How is overcurrent protection calculated?
The feeder overcurrent protection device must be sized not less than 125% of 184 amperes, So, overcurrent protection device size = 184 amperes x 125% = 230 amperes. According to Section 240-6(a) for “Standard Ampere Ratings of overcurrent devices”, we must select a minimum 250 ampere overcurrent protection device.
What is TMS in overcurrent relay?
Time Multiplier Setting used to change the value of operation of the relay. If it is more the relay will take more time to operate and vice versa. Changing the position of TMS setting, changes the distance between the contact of the rotating disk and the coil.
What is PSM and TSM in relay?
Time Setting Multiplier (TSM): The arrangement provided for setting the operating time of protective relay from zero sec to maximum permissible time for a specified current setting is known as time setting multiplier. Plug Setting Multiplier (PSM): It is the ratio of fault current in relay coil to pick-up current.
What is inverse time characteristic?
At lower over current levels, the circuit breaker must wait for some time to see if this temporary fault. After letting the overcurrent flow for some time, if it is still experiencing some fault current then the interrupting circuit breaker must break the circuit. This is called the inverse time characteristic.