Product Overview
The LXK series unitary zero sequence current transformer is an indoor epoxy resin cast current transformer designed for cable earth fault protection, zero sequence current detection, and residual current monitoring in small-current grounding systems. It is suitable for indoor AC power systems with rated frequency of 50Hz or 60Hz and rated voltage up to 35kV.
The LXK series adopts a unitary non-split ring-core structure. The magnetic core and secondary winding are fully enclosed by epoxy resin casting. Unlike open-type zero sequence current transformers, the standard LXK structure is not cut into two halves. During installation, the cable group or busbar group must pass through the central window of the transformer. This integrated structure provides stable magnetic performance and is suitable for applications requiring higher consistency and reliable zero sequence current detection.
For projects where the cable has already been installed and cannot be disconnected, the LXK structure can also be customized as an open-type version with a clamping structure. The standard catalogue model, however, is recommended as an integrated unitary type when installation conditions allow the cable group to pass through the transformer window.
Product Type
| Item | Specification |
|---|---|
| Product name | LXK Series Unitary Zero Sequence Current Transformer |
| Model series | LXK-80, LXK-100, LXK-120, LXK-140, LXK-150, LXK-160, LXK-180, LXK-200, LXK-240, LXK-260 |
| Product structure | Indoor epoxy resin cast unitary ring-core zero sequence current transformer |
| Standard structure | Non-split integrated type; cable or busbar passes through during installation |
| Optional structure | Open-type clamping version can be customized for retrofit installation |
| Inner diameter range | φ80 to φ260; common options include φ80, φ100, φ120, φ140, φ150, φ160 and φ180 |
| Rated insulation level | 0.72/3kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 5A or 1A |
| Protection class | 10P5 to 10P20 according to model and specification |
| Installation location | Indoor |
| Typical applications | Cable earth fault protection, zero sequence current detection, residual current monitoring, grounding fault alarm and trip circuits |
Product Display
Main Applications
- Indoor cable earth fault protection for systems up to 35kV
- Small-current grounding system zero sequence current detection
- Residual current monitoring in cable feeder circuits
- Single-phase grounding fault alarm and trip protection
- Ring network cabinets, distribution cabinets, and switchgear protection panels
- Motor feeder, generator feeder, and cable branch protection systems
- Relay protection circuits requiring 5A or 1A secondary current input
Key Technical Features
- Unitary ring-core design: The standard LXK series is an integrated non-split structure, which supports stable magnetic performance and accurate residual current detection.
- Epoxy resin casting: The core and secondary winding are encapsulated by epoxy resin to improve insulation strength, moisture resistance, and mechanical protection.
- Wide aperture range: Multiple inner diameters are available from φ80 to φ260, covering different cable group and busbar layouts.
- Zero sequence protection function: The transformer detects unbalanced residual current caused by grounding faults and outputs a secondary signal for protection relays.
- 5A or 1A secondary output: Compatible with common relay protection devices, monitoring units, and current input modules.
- Optional open-type customization: For retrofit projects, the unitary design can be customized into a split clamping structure when required.
Working Principle
The LXK zero sequence current transformer measures the vector sum of all phase currents passing through its window. During normal operation, the vector sum of the phase currents is close to zero. When a single-phase ground fault, insulation fault, or leakage current occurs, the current balance is broken and zero sequence current appears. The transformer converts this residual current into a secondary current signal for relay protection, alarm, or monitoring.
For correct operation, all protected phase conductors must pass through the same transformer window in the same direction. The primary insulation is provided mainly by the cable itself. The transformer product is primarily assessed for the insulation performance of the secondary winding and the cast-resin body.
Model Designation
The model code can be interpreted as follows:
| Code | Meaning |
|---|---|
| L | Current transformer |
| X | Zero sequence current transformer type |
| K | Unitary / integrated structure series |
| 80 / 100 / 120 / 140 / 150 / 160 / 180 / 200 / 240 / 260 | Nominal inner window diameter or model size code |
| Dimension group, such as 120/210×65 | Inner diameter / outer diameter and body thickness reference |
Structure Introduction
The standard LXK zero sequence current transformer is a non-split integrated structure. The magnetic core is not cut into two halves. The complete ring core and secondary winding are cast in epoxy resin, forming a compact and mechanically stable annular body. During installation, the three-phase cable group or busbar group passes through the central window of the transformer.
This structure is suitable for new installations, cabinet assembly, and cable systems where the conductor can be passed through the transformer before final termination. Compared with an open-type split-core structure, the unitary LXK type provides a continuous magnetic path and is suitable for applications requiring stable detection accuracy. If site installation requires opening installation, an open-type clamping version can be customized.
Technical Data
| Item | Specification |
|---|---|
| Model series | LXK-80 to LXK-260 |
| Product type | Indoor epoxy resin cast unitary zero sequence current transformer |
| Rated voltage application | Suitable for indoor small-current grounding systems up to 35kV |
| Rated insulation level | 0.72/3kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 5A or 1A |
| Protection class | 10P5, 10P10, 10P15, 10P20 according to selected model |
| Ambient temperature | -25°C to +40°C |
| Insulation structure | Epoxy resin cast insulation |
| Primary insulation | Provided by the cable or busbar insulation system |
| 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 Range | Common Current
Ratio Options |
Rated Secondary
Current |
Protection
Class Range |
Rated
Output Range |
|---|---|---|---|---|
| LXK-80 / LXK-100 | 50/5 to 250/1 | 5A or 1A | 10P5 to 10P10 | 5VA to 2.5VA according to specification |
| LXK-120 | 50/5 to 250/1 | 5A or 1A | 10P5 to 10P20 | 10VA to 2.5VA, or 15VA to 5VA depending on structure |
| LXK-150 / LXK-160 | 50/5 to 250/1 | 5A or 1A | 10P5 to 10P20 | 10VA to 2.5VA, or 15VA to 5VA depending on model |
| LXK-180 / LXK-200 | 50/5 to 250/1 | 5A or 1A | 10P5 to 10P20 | 10VA to 2.5VA, or 15VA to 5VA depending on model |
| LXK-240 / LXK-260 | 50/5 to 250/1 | 5A or 1A | 10P5 to 10P20 | 15VA to 5VA according to specification |
Note: The catalogue table contains multiple combinations of current ratio, protection class and rated output. Final parameters should be confirmed according to the selected model, relay burden and technical agreement.
Service Conditions
- Installation location: indoor
- Rated frequency: 50Hz / 60Hz
- Applicable system: small-current grounding systems up to 35kV
- 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 group should pass through the circular 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 LXK series unitary zero sequence current transformers are 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
The standard LXK series is an integrated circular structure. The protected three-phase cable group or busbar group must be routed through the central window during installation. It is suitable for new cabinet assembly, planned cable routing, or systems where the cable can pass through the CT before final termination.
Model Size and Dimension Reference
| Model | Type
Dimension Code |
φd | φD | C | A | B | E | L |
|---|---|---|---|---|---|---|---|---|
| LXK-80 | 80/165×57 | 80 | 165 | 57 | 130 | 120 | 102 | 185 |
| LXK-100 | 100/180×55 | 100 | 177 | 55 | 130 | 118 | 114 | 203 |
| LXK-100 | 100/180×57 | 100 | 180 | 57 | 130 | 120 | 113 | 203 |
| LXK-120 | 120/204×57 | 120 | 204 | 57 | 130 | 120 | 121 | 223 |
| LXK-120 | 120/210×65 | 120 | 210 | 65 | 130 | 125 | 123 | 228 |
| LXK-120 | 120/210×100 | 120 | 210 | 100 | 130 | 163 | 123 | 228 |
| LXK-120 | 120/250×80 | 120 | 250 | 80 | 190 | 174 | 153 | 268 |
| LXK-150 | 150/235×57 | 150 | 235 | 57 | 190 | 151 | 150 | 267 |
| LXK-150 | 150/280×80 | 150 | 280 | 80 | 190 | 174 | 158 | 297 |
| LXK-160 | 160/250×80 | 160 | 250 | 80 | 190 | 174 | 156 | 290 |
| LXK-180 | 180/265×57 | 180 | 265 | 57 | 190 | 161 | 165 | 298 |
| LXK-180 | 180/310×80 | 180 | 310 | 80 | 260 | 164 | 190 | 365 |
| LXK-200 | 200/330×80 | 200 | 330 | 80 | 260 | 164 | 200 | 365 |
| LXK-240 | 240/350×80 | 240 | 350 | 80 | 260 | 164 | 220 | 395 |
| LXK-260 | 260/370×80 | 260 | 370 | 80 | 260 | 164 | 229 | 410 |
Unit: mm. Final dimensions, mounting hole positions, terminal box position and installation clearance are subject to the approved outline drawing.
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, inner diameter, body thickness, current ratio, secondary current, protection class and rated output before installation.
- Check that the cable group can pass through the selected circular window with sufficient clearance and bending radius.
- Select the model according to both cable outside diameter and available cabinet depth.
- 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, such as LXK-80, LXK-120, LXK-180, LXK-240 or LXK-260
- Dimension code, such as 120/210×65 or 180/310×80
- Required structure: standard unitary type or customized open-type clamping structure
- Rated current ratio, such as 100/5, 200/5, 300/5, 50/1 or 100/1
- Rated secondary current: 5A or 1A
- Required protection class: 10P5, 10P10, 10P15 or 10P20
- Rated output / burden in VA
- Maximum outside dimension of the protected cable group
- Relay model, protection scheme and grounding fault detection requirement
- Installation environment, cabinet layout, quantity, drawings, labels, certificates and packaging requirements
Selection Guidelines
- Confirm cable group size: Select an inner diameter that allows all protected phase conductors to pass through the same CT window.
- Confirm installation method: Use the standard unitary LXK type when the cable can be routed through the CT before final termination.
- Consider open-type customization: If the cable is already installed and cannot be disconnected, specify a customized open-type clamping structure.
- Confirm body thickness: Select 55, 57, 65, 80 or 100 mm body structures according to output requirement and cabinet depth.
- 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 to 10P20 according to protection circuit requirements.
- Check rated burden: Ensure the relay input, secondary wiring and terminal burden do not exceed the rated output.