10.12. Configuring the user defined circuit breaker protection

In the circuit breaker model selection user can select “User Defined” optio. This option is added if the user did not find required circuit breaker in EA-PSM library. The user can easily define any circuit breaker characteristic. User defined circuit breaker configuration window is shown in the following figure:

In the configuration window, the user has to define nominal circuit breaker IN and three points (current on the x axis and time on the y axis) shown in the right side of Figure 9.24 . Each current point is defined as a coefficient, which is multiplied by the nominal current, and each time point is defined in seconds.

List of values to be defined:

IN – nominal current;
I1 = IN * k1– coefficient k1 for a vertical Long Time Pickup line;
t1 at I²t – time setting for overload stage or Long Time Band at this time breaker will trip when current is I1;
I2 = IN * k2 - coefficient k2 for a vertical Short Time Pickup line;
t2 – time setting for a Short Time Band if “I²t” is selected, short time band will have I2t mode like Long Time Band;
I3 = IN *k3 - coefficient k3 for a vertical Instantaneous Pickup line;
t3 – time setting for an Instantaneous Trip line;

Meaning of other coefficients in the protection tab and further explanation:

Ka – Reserve coefficients;
Kp – Transitional process coefficient;
Kg – Protection return coefficient;

The overcurrent protection current settings value

could be calculated as:

There

is the long term feeder maximum current. The coefficient

is related to the current measurement error of the current transformer and protection relay. For example, the current transformer current measurement error is 10%, protection relay measurement error equals to 5%, thus, the coefficient

Coefficient is equal to the ratio of current reset level (value) with current pickup level (value). Typical value is .
Pickup Level (value) of Actuating Signal: The value of actuating quantity (voltage or current), which is on threshold above which the relay initiates to be operated. If the value of actuating quantity is increased, the electromagnetic effect of the relay coil is increased and above a certain level of actuating quantity the moving mechanism of the relay just starts to move.
Reset Level (value) : The value of current or voltage below which a relay opens its contacts and comes in the original position.
Coefficient represents current pick up value margin due to current transient. For example, instantaneous overcurrent (OC) protection would have for motor start protection at the same time OC relay operating time equals to 50ms. Different operating time yields different OC protection margin and value.
Operating Time of Relay- Just after exceeding pickup level of actuating quantity the moving mechanism (for example rotating disc) of relay starts moving and it ultimately closes the relay contacts at the end of its journey. The time which elapses between the instant when actuating quantity exceeds the pickup value to the instant when the relay contacts close.