What is negative sequence over current?

− Negative sequence overcurrent relays are used to detect unbalanced load on a generator which may cause exces- sive rotor heating. The relay is also used to detect unbal- anced load currents in motors. − Earth-fault detection in solidly earthed system. − The relay has I-Start, I-Alarm, I-Trip and Blocking functions.

How do you calculate negative sequence current?

Negative Sequence Current (2OC) calculator uses Negative Sequence Current = A-Phase Current/3 to calculate the Negative Sequence Current, The Negative Sequence Current (2OC) formula is defined as consists of balanced three-phase voltage and current phasors which are exactly at 120 degrees apart rotating …

What is the effect of negative sequence current in induction motor?

induction motor Performance of these induction motors is affected by the unbalance in bus voltage caused by negative sequence currents, which produces an air gap flux rotating opposite to the direction of rotor thereby heats up the rotor and generates a breaking torque.

What is negative sequence current in a motor?

Negative-sequence overcurrent or current unbalance relays are also common for motor protection. These relays are required to provide thermal protection against excessive current induced on the rotor. As such, these elements are typically set with a relatively long delay.

Why is negative sequence current bad?

The flow of negative sequence currents in electrical machines (generators and motors) is undesirable as these currents can generate high and possibly dangerous temperatures in a very short period of time which can damage the insulation of the machines causing them to fail prematurely.

How fault causes negative phase sequence current?

If an alternator is subjected to an unbalanced load situation, connected to non-linear loads or an asymmetrical fault condition, then the resulting state is described as having a Negative Phase Sequence component. Under these conditions, a Negative Phase Sequence Current [symbolised as I2] will exist.

What is the difference between positive and negative sequence?

Physically, in a three phase system, a positive sequence set of currents produces a normal rotating field, a negative sequence set produces a field with the opposite rotation, and the zero sequence set produces a field that oscillates but does not rotate between phase windings.

What is negative sequence overcurrent protection?

Negative Sequence Protection fills in the protection gap left by Overcurrent and Earth Fault protection, by catching the scenarios of broken conductors or ungrounded faults such as line to line faults.