The shunt capacitor bank of low voltage reactive-power compensation device in UHV system mainly plays important role in improving voltage and power factor in the high load power transmission.Shunt capacitor bank in UHV Changzhi power station has large capacity and many unit numbers.The double difference and double time setting are adopted for the bridge type differential current protection.The comparison and analysis between the actually measured maximum value through the bridge differential current and the double time setting proves the rationality of the bridge differential current protection using double difference and double time setting.