Overview

The LJM-1, LJM-2, LJM-3, and LJM-3L Bus-Type Zero Sequence Current Transformers are advanced indoor transformers, and are designed for accurate zero-sequence current measurement in power systems (Accurate Earthing Protection). These Zero Sequence Current Transformers feature a robust bus-type structure, making them ideal for applications involving three-phase AC generators and motors requiring zero-sequence protection.

With a rated frequency of 50Hz or 60Hz and a rated voltage of 15kV or below (commonly used for 6kV, 10kV, and 15kV systems), the LJM series transformers ensure reliable fault detection and system monitoring. They are specifically paired with the DD11/60 relay for enhanced zero-sequence protection, ensuring safe and efficient operation in power distribution networks.

Type Designation Explanation

The following is the type designation for the LJM-1, LJM-2, and LJM-3 Zero Sequence Current Transformers:

• L: Current transformer
• J: Earthing protection
• M: Busbar type
• 1, 2, 3: Rated voltage classification

Note: For special requirements or specific customizations, please contact our technical team for tailored solutions.

Operating Conditions for LJM

1. Altitude: Not exceeding 1000 meters.
2. Ambient Temperature: Between -5°C and +40°C.
3. Relative Humidity: Not exceeding 85% at 20°C.
4. Installation Environment: Free from severe gases, vapors, chemical deposits, pollution, and other explosive or corrosive substances that could affect the transformer’s insulation.

Structure of LJM Bus-Type Zero Sequence Current Transformer

The LJM Zero Sequence Current Transformer features a bus-type structure, equipped with primary busbars to facilitate convenient installation. When the primary zero-sequence current reaches the preset threshold, the transformer provides an accurate secondary current output to activate the relay, achieving reliable protection for the electrical system.

Technical Data for LJM

Standards: Current transformers are designed in accordance with the Shanghai Standards Q/JB 3380-84.

Type	LJM-1	LJM-2	LJM-3
Rated primary current (A)	1750	3000	4000
Rated secondary current (A)	5	5	5
Frequency (Hz)	50	50	50
Ith (kA)	24	48	72
Idyn (kA)	2.5 Ith	2.5 Ith	2.5 Ith
Max. short-circuit impulse current (kA)	165	165	165
Unbalancing Voltage (mV)	<60	<85	<100
Insulation level (kV)	6/32	10/42	15/55

For special customizations or technical requirements, please contact our support team.

Notes:

1. For secondary windings connected in parallel, the exciting resistance must be greater than 10Ω.
2. The rated voltage is available in three classifications: 6kV, 10kV, and 15kV.

Outline and Dimensions of Installation

LJM-1 1750A Bus-Type Zero Sequence Current Transformer indoor type

LJM-2 3000A Bus-Type Zero Sequence Current Transformer

LJM-3 4000A Bus-Type Zero Sequence Current Transformer

LJM-3L 5000A Bus-Type Zero Sequence Current Transformer

When ordering, please specify the following:

1. Insulation level;
2. Current ratio;
3. Accurate level and rated secondary load;
4. Use environment;
5. For special requirements, please contact our technical team.

FAQs for LJM Bus-Type Zero Sequence Current Transformers

1. What are the key applications of the LJM Bus-Type Zero Sequence Current Transformers?
   These transformers are designed for zero-sequence current measurement, fault detection, and relay protection in medium-voltage power systems.
2. What voltage levels are supported by the LJM series?
   The LJM series supports voltage levels of 6kV, 10kV, and 15kV, with a maximum rated voltage of 15kV.
3. Can the LJM transformers be customized for specific needs?
   Yes, the transformers can be customized for insulation levels, current ratios, and specific secondary load requirements to suit diverse operational needs.
4. Which relay is compatible with the LJM transformers for protection purposes?
   The LJM transformers are specifically paired with the DD11/60 relay for advanced zero-sequence protection and fault monitoring.
5. What is the maximum short-circuit current the LJM series can handle?
   The LJM transformers can handle maximum short-circuit impulse currents up to 165kA, providing robust protection in fault conditions.
6. Are the LJM transformers suitable for outdoor installations?
   No, the LJM series is designed for indoor use only and requires clean environments free from corrosive gases, pollutants, or significant dust.

• 3 Voltage Transformer Faults and Solutions: Ensuring Accurate Measurement and Protection
• Single-Phase Voltage Transformers Role, Function, and Importance in Power Systems
• Analysis of the Impact of Incorrect CT S1 and S2 Connections and Reversed Input Lines
• Common Fault Handling for Current and Voltage Transformers
• Causes and Solutions for False Fault Alarms in Zero-Sequence Current Transformers
• Analysis of the Impact of Current Transformer Faults on Energy Meter Accuracy