Three phase motor differential relay testing can be done 
with single phase test kit.

There are two type of relay testings:
1) Primary injection : In this testing entire system 
(including relay, control wiring and power wiring get 
checked),
2) Secondary injection : In this testing generally we check 
relay only. 

By using single phase test kit:
1) Primary injection : 
a) Carryout shorting of all three phases of motor winding 
by using short link for individual phases seperately. 
b) Inject current by using current injection device (for 
inzone and outzone fault)
3) Check stability of relay for outzone fault and operation 
of relay for inzone fault.

2) Secondary injection :
Directly inject fault current in relay terminal and check 
proper operation of relay. 

Santosh Kawade 
9224 69 3116