Product Overview
The LXKW-120/75 and LXKW-120/57 indoor cast-resin open zero sequence current transformers are designed for zero sequence current detection, residual current monitoring, and grounding fault protection in indoor power distribution systems. The series adopts an indoor cast-resin insulated open structure and is suitable for 50Hz or 60Hz AC systems requiring relay protection signals.
Both models use a large circular window with a φ120 mm inner diameter. The main difference is the body thickness and output capability: LXKW-120/75 has a thicker structure and higher rated output, while LXKW-120/57 provides a slimmer body for applications with limited installation depth. The products are suitable for three-phase cable groups, cable outlet protection, switchgear protection cabinets, and residual current monitoring systems.
Product Type
| Item | Specification |
|---|---|
| Product name | Indoor Cast-Resin Open Zero Sequence Current Transformer |
| Model series | LXKW-120/75, LXKW-120/57 |
| Product structure | Indoor cast-resin open-type zero sequence current transformer |
| Window size | φ120 mm inner window |
| Body thickness options | 75 mm and 57 mm structure variants |
| Rated insulation level | 0.72/3kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 5A or 1A |
| Protection class | 10P5 / 10P10 |
| Installation location | Indoor |
| Typical applications | Zero sequence current detection, earth fault protection, residual current monitoring, cable feeder protection |
Product Display
Main Applications
- Indoor cable feeder earth fault protection
- Zero sequence current detection in three-phase cable systems
- Residual current monitoring for switchgear and protection cabinets
- Small-current grounding system protection
- Single-phase grounding fault alarm and trip circuits
- Ring network cabinet, distribution cabinet, and medium-voltage cable outlet protection
- Relay protection input for 5A or 1A secondary current circuits
Key Technical Features
- Two structure variants: LXKW-120/75 and LXKW-120/57 use the same φ120 mm window but different body thickness and rated output ranges.
- Open-type structure: The open current transformer body supports convenient installation around cable groups or cabinet conductors.
- Cast-resin insulation: The indoor cast-resin body supports insulation performance, mechanical stability, and long-term cabinet service.
- Zero sequence current detection: Detects residual current generated by grounding faults and outputs a signal to relay protection devices.
- 5A or 1A secondary output: Compatible with common relay, protection, and monitoring input requirements.
- 10P protection classes: 10P5 and 10P10 output options are available according to current ratio, model thickness, and rated burden.
Working Principle
The LXKW-120 series zero sequence current transformer measures the vector sum of the currents passing through its window. During normal three-phase operation, the vector sum of the phase currents is close to zero, and the transformer secondary output is very small. When a single-phase ground fault or insulation fault occurs, the system current becomes unbalanced and zero sequence current appears. The transformer converts the residual current into a secondary current signal for the connected relay or monitoring device.
For correct zero sequence protection, all phase conductors of the protected circuit should pass through the same transformer window in the same direction. The secondary terminals are marked as S1 and S2 according to the wiring diagram, and should be connected according to the relay protection scheme.
Model Designation
The model code can be interpreted as follows:
| Code | Meaning |
|---|---|
| L | Current transformer |
| X | Zero sequence current transformer type |
| K | Open-type / opening structure |
| W | Design structure code for this product series |
| 120 | φ120 mm inner window diameter |
| 75 / 57 | Body thickness structure code |
Technical Data
| Item | Specification |
|---|---|
| Model | LXKW-120/75, LXKW-120/57 |
| Product type | Indoor cast-resin open zero sequence current transformer |
| Rated insulation level | 0.72/3kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 5A or 1A |
| Protection class | 10P5 / 10P10 |
| Ambient temperature | -25°C to +40°C |
| Insulation structure | Indoor cast-resin insulation |
| Applicable standards | GB 20840.1-2010, GB 20840.2-2014; customer-specific requirements can be confirmed by agreement |
Rated Current Ratio and Output Reference
| Model | Rated
Current Ratio |
Rated
Secondary Current |
Rated
Output for 10P5 (VA) |
Rated
Output for 10P10 (VA) |
|---|---|---|---|---|
| LXKW-120/75 | 50/5 | 5A | 1.5 | – |
| 75/5 | 5A | 2.5 | 0.5 | |
| 100/5 | 5A | 3.75 | 1 | |
| 150/5 | 5A | 5 | 2.5 | |
| 200/5 | 5A | 7.5 | 3.75 | |
| 300–400/5 | 5A | 10 | 5 | |
| 50/1 | 1A | 1.5 | – | |
| 75/1 | 1A | 2.5 | 0.5 | |
| 100/1 | 1A | 3.75 | 1 | |
| 150/1 | 1A | 5 | 2.5 | |
| LXKW-120/57 | 50/5 | 5A | 0.5 | – |
| 75/5 | 5A | 1 | – | |
| 100/5 | 5A | 1.5 | 0.5 | |
| 150/5 | 5A | 2 | 1 | |
| 200/5 | 5A | 3.75 | 1.5 | |
| 300–400/5 | 5A | 5 | 2 | |
| 50/1 | 1A | 1 | – | |
| 75/1 | 1A | 1.5 | – | |
| 100/1 | 1A | 2 | 0.5 | |
| 150/1 | 1A | 2.5 | 1 |
Note: If required parameters exceed the listed catalogue range, current ratio, protection class and rated output can be confirmed through technical agreement.
Service Conditions
- Installation location: indoor
- Rated insulation level: 0.72/3kV
- Rated frequency: 50Hz / 60Hz
- Ambient temperature: -25°C to +40°C
- The installation environment should be free from severe vibration, corrosive gas, conductive dust, explosive medium, heavy moisture and serious pollution.
- All phase conductors of the protected circuit should pass through the same transformer window in the same direction.
- The cable or conductor group should pass through the window without mechanical stress on the transformer body.
- For special cable diameter, relay model, wiring distance, burden or protection setting requirements, technical confirmation is recommended before ordering.
Standards and Compliance
The LXKW-120 open zero sequence current transformer series is designed according to GB 20840.1-2010 and GB 20840.2-2014, and can be supplied according to customer-specific project requirements. Final current ratio, protection class, rated output, routine test items, nameplate data and wiring requirements should be confirmed in the technical agreement.
Installation and Dimensions
Overall Dimensions Reference
| Drawing
No. |
Model | Inner
Window Diameter |
Outer
Diameter Reference |
Overall
Height |
H1
(mm) |
H2
(mm) |
H3
(mm) |
|---|---|---|---|---|---|---|---|
| OTC.300.1133.1 | LXKW-120/57 | φ120 mm | φ187 mm | 250 mm | 57 | 71 | 88 |
| OTC.300.1133.2 | LXKW-120/75 | φ120 mm | φ187 mm | 250 mm | 75 | 89 | 106 |
Unit: mm. Final dimensions, mounting hole positions, terminal box position and installation clearance are subject to the approved outline drawing.
The LXKW-120/75 and LXKW-120/57 models are installed around the protected conductor group. The φ120 mm window allows the three-phase cable group to pass through the transformer. Secondary terminals should be wired according to the protection relay diagram. The product should be fixed on the cabinet base or mounting bracket to prevent movement and vibration during operation.
Wiring Reference
| Terminal | Function | Wiring Note |
|---|---|---|
| S1 | Secondary output terminal | Connect to relay or monitoring input according to polarity requirement |
| S2 | Secondary output terminal | Connect to relay or monitoring return terminal |
| Ground / shield terminal | Grounding reference where provided | Connect according to project grounding and protection scheme |
Connection and Wiring Notes
- All phase conductors of the protected circuit should pass through the same window in the same direction.
- Do not pass only one phase conductor through the window when the transformer is used for zero sequence protection.
- Connect secondary terminals S1 and S2 according to the relay wiring diagram and polarity requirements.
- Check secondary wiring continuity, terminal tightening and relay setting before energizing.
- The secondary circuit of a current transformer must not be open-circuited when the primary circuit is energized.
- Secondary grounding and terminal protection should comply with project specifications and local electrical regulations.
Installation and Safety Notes
- Confirm the model, window diameter, body thickness, current ratio, secondary current, protection class and rated output before installation.
- Check that the cable or conductor group can pass through the φ120 mm window with sufficient clearance.
- Select LXKW-120/57 when cabinet depth is limited and lower rated output is acceptable.
- Select LXKW-120/75 when higher rated output is required or when the standard thicker structure is preferred.
- Install the transformer in an indoor cabinet or cable compartment according to the approved drawing.
- Keep the conductor group centered as far as possible in the window to support stable residual current detection.
- Check mounting bolts, terminal marks, secondary wiring and relay connection before commissioning.
- Installation, testing and maintenance should be performed by qualified electrical personnel.
Ordering Information
Please provide the following information when ordering or requesting a quotation:
- Product model: LXKW-120/75 or LXKW-120/57
- Rated current ratio, such as 100/5, 200/5, 300/5, 400/5, 50/1 or 100/1
- Rated secondary current: 5A or 1A
- Required protection class: 10P5 or 10P10
- Rated output / burden in VA
- Maximum outside dimension of the three-phase cable or conductor group
- Relay model, protection scheme and grounding fault detection requirement
- Installation environment, cabinet layout, quantity, drawings, labels, certificates and packaging requirements
Selection Guidelines
- Confirm application: Select LXKW-120 series for zero sequence current detection and earth fault protection in indoor cable or conductor systems.
- Confirm cable group size: Ensure the complete protected conductor group can pass through the φ120 mm window.
- Select thickness variant: Choose LXKW-120/57 for reduced installation depth or LXKW-120/75 for higher output capability.
- Confirm current ratio: Select the current ratio according to relay input and protection setting requirements.
- Select secondary current: Choose 5A or 1A according to the connected relay or monitoring device.
- Choose protection class: Select 10P5 or 10P10 according to protection circuit requirements.
- Check rated burden: Ensure the relay input, secondary wiring and terminal burden do not exceed the rated output.
- Confirm installation space: Check H1, H2, H3 dimensions, mounting position and cable bending space before ordering.