Negative Sequence Voltage Calculator
Calculate negative sequence voltage from three-phase voltages using symmetrical components. Helps assess unbalance and protect rotating machines.
motor voltage imbalance calculator
When ut come to unbalanced voltages, three-phase voltages cause negative sequence voltage. The measured value is obtained in symmetrical components and, in negative sequence, the unbalance component V 2 measures the unbalance. A large negative sequence factor (NSF%) may have a devastating effect on motors, leading to the overheating of such motors and lowered efficiency.
Formula & Table Summary:
- Negative Sequence: V₂ = (Va + a²Vb + aVc)/3
- Positive Sequence: V₁ = (Va + aVb + a²Vc)/3
- NSF% = |V₂| / |V₁| × 100
- Limit: NSF < 2–3% (per NEMA MG1)
electrical fault negative sequence
The negative-sequence-use the three phase voltages to calculate the negative sequence voltage (V 2 ) via symmetrical component theory. Very large negative sequence voltages Reflect imbalance in the system and potentially destroy the motor and generators. The Negative Sequence Voltage Calculator calculates the negative sequence component of a three-phase system based on the symmetrical component theory. An example is that voltage unbalance, resulting in the presence of negative-sequence voltages, acts against the rotating field in machines, resulting in overheating, pulsations in the machine torque, and a shortened motor life.
unbalanced three-phase voltage tool
| Va (V) | Vb (V) | Vc (V) | V₁ (Pos Seq) | V₂ (Neg Seq) | NSF (%) |
|---|---|---|---|---|---|
| 230 | 230 | 230 | 230∠0° | 0 | 0.0 |
| 230 | 225 | 235 | 230∠-1° | 2.5∠-120° | 1.1 |
| 230 | 210 | 240 | 227∠-2° | 6.8∠60° | 3.0 |
| 230 | 200 | 245 | 225∠-3° | 12.2∠90° | 5.4 |
Frequently Asked Questions - Negative Sequence Voltage Calculator:
What is negative sequence voltage?
It is the component of unbalanced three-phase voltage that rotates opposite to the positive sequence.
How is negative sequence voltage calculated?
Using symmetrical components: V2 = 1/3 (Va + a²Vb + aVc), with a = e^(j120°).
What is the negative sequence factor (NSF)?
NSF (%) = |V2| / |V1| × 100, showing the ratio of negative to positive sequence voltage.
What causes negative sequence voltage?
Unbalanced supply voltages, unequal loads, or system faults.
Why is negative sequence harmful to motors?
It induces reverse magnetic fields, causing overheating and torque pulsations.
What is the acceptable limit of NSF?
Usually below 2–3% for motors, per NEMA MG1 standards.
Can unbalance reduce motor life?
Yes, even a 2–3% voltage unbalance can cut motor life by 30–50%.
Is NSF used in protection relays?
Yes, negative sequence relays protect generators and motors from unbalance damage.
How do you measure NSF in practice?
Measure three-phase voltages with a power quality analyzer, then compute sequence components.
Can capacitor banks cause negative sequence?
Yes, if banks are unevenly distributed across phases, they can increase voltage unbalance.
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