What is negative sequence current in a motor?
The negative-sequence current produces a reverse rotating magnetic field in the air gap. This field produces a shaft torque pulsation at twice line frequency. The magnitude of the torque is proportional to the per unit negative-sequence current in the stator. The pulsations are transmitted to the stator.
What is negative sequence overcurrent?
− 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.
What is negative sequence current protection?
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.
What causes negative sequence currents?
Causes and Effects of Negative Sequence Components Unbalanced loads in the system. Unbalanced system faults (line to ground faults, two phase faults, triple line to ground faults, double line to ground faults) Open phases (open circuit faults)
What is negative sequence voltage?
Negative sequence voltage creates negative sequence current in motors that creates flux in the opposite direction to the positive sequence flux. This will cause additional heating in motor. Negative sequence is used in directional relaying and unbalance protection.
What is negative sequence overvoltage?
Overview. The “Overvoltage protection with negative sequence voltage” function is used to monitor the power system and electric machines for voltage unbalances and establish a release criterion of overcurrent protection for unbalanced faults.
Why do negative phase sequences occur?
Negative sequence components are most commonly generated when the line-to-line voltages applied to a three phase motor are unequal, which can happen when other loads on the network are not balanced across all three phases.
What is the value of zero sequence current?
Q.
How do you calculate negative phase sequence current?
To establish the level of Negative Phase Sequence current component associated with this unbalanced load condition: Divide this 25% by 3. Negative Phase Sequence Condition is therefore approximately 8%. For further guidance on Unbalanced Load conditions, refer to AGN017 Unbalanced Loads.
What is a negative sequence voltage in a motor?
A negative sequence voltage of 2% may give rise to a negative sequence motor current of 10-15%. Negative sequence current protection should be included if there is a risk of uneven loading in exceed of the maximum permissible continuous value.
What is negative sequence component in AC power system?
It specifies that the current is flowing through source to load . Negative sequence component:- it represents three equal phasors, phase displaced by 120° with each other,and has phase sequence opposite to that of the original phasors. It specifies that current is flowing from load to source.
What is positive sequence and negative sequence in a generator?
These are positive-, negative- and zero-sequence components. The positive sequence component of current or voltage has the same rotation as the power system. This component represents balanced load. If the generator phase currents are equal and displaced by exactly 120°, only positive-sequence current will exist.
What is negnegative sequence current protection?
Negative sequence current protection should be included if there is a risk of uneven loading in exceed of the maximum permissible continuous value. The calculated negative sequence current is compared with the set operate value for the I_Alarm and the I_Start function.