三相四线电能表无功功率表达式( ):
A.P=UaIacosφa+UbIbcosφb+UcIccosφc;
B.P=UaIasinφa+UbIbsinφb+UcIcsinφc
C.P=UaIactgφa+UbIbctgφb+UcIcctgφc
D.P=3UIctgφa
正确答案是B