Please describe the current setting for the timing element in the K2CA Over-Current Relay(OCR).

The operating current for the timing element is usually set to approximately 150% of the current value for the contract power. The tap value is obtained from the following formula:

ITAP: The setting tap value (A) for the OCR timing element
I1: The current value for the contract power (equals contract power (kW)/√3 x 6.6 (kV))
ICT: Primary rated current of the current transformer (secondary current is 5 A)

Because the tap value in the K2CA Series can be set in relatively fine increments of 3, 3.5, 4, 5.4, 5, or 6 A, it is quite easy to make the 150% setting to provide optimal overload protection.

The following table shows the relationship between the contract power and the setting tap. The α value in this table is the proportion of the current for the contract power and the OCR operating current, indicating the tap values near the 150% point. The tap value can be easily changed by turning a rotary switch. There is no need to insert a spare tap to prevent an open circuit on the CT2 side as in previous systems.

Contract Power vs. K2CA Timing Element Current Setting

Contract
power
(kW)
CT1 primary current (A)
5 10 15 20 30 40
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
50 6 136 3 136        
3.5 159
100   6 138 3.5 121 3 138    
4 138
4.5 155 3.5 161
5 172
200       6 137 3.5 120 3 137
4 137
4.5 154 3.5 160
5 171
300         6 137 4 122
4.5 137
5 153
500            
750            
1,000            
1,500          
Contract
power
(kW)
CT1 primary current (A)
50 75 100 150 200 300
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
Tap
(A)
α
(%)
50            
100            
200 3 171          
300 3.5 134 3 172        
4 153
4.5 172
500 6 137 3.5 120 3 137      
4 137
4.5 154 3.5 160
5 172
750   6 137 4 122 3 137    
4.5 137
3.5 160
5 152
1,000     6 137 3.5 120 3 137  
4 137
4.5 154 3.5 160
5 171
1,500       6 137 4 122 3 137
4.5 137
3.5 160
5 153
 

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