AC Power tolerances

• Current and voltages drawn on a three phase supply should be equal
  
  
• However electrical equipment can handle some small fluctuations, provided these are within the following specifications
  
  
• Voltage imbalance < 2% Current imbalance < 10%
  
  
• Any imbalance above the specifications must be corrected
  
  

Voltage Imbalance

• Find the voltage imbalance for the following three phase circuit
  
  
• Supply Voltage 208V Voltage reading, for each leg 211, 206, 214
  
  
• Step 1: find average Voltage
  
  
• 211 + 206 + 214 = 210.33V
  3
  

• Step 2: Find Maximum Deviation Average
  
  
• 211 - 210 .33 = 0.67V
  
  
• 206 – 210.33 = 4.33V
  
  
• 214 – 210.33 = 3.67V
  
  
• Step 3: Find the Voltage Imbalance
  
  
  
• % Imbalance = 100 x max deviation from average
  average voltage
  
  
• % Imbalance = 100 x 4.33
  210.33
  
• %Imbalance =2.06%
  
  

Current imbalance is usually a result of voltage imbalance