LQZJ-0.66 লো-ভোল্টেজ ইনডোর কারেন্ট ট্রান্সফরমার এপক্সি রেজিন কাস্ট

2. Model Designation & Variants

2.1 Model Code Explanation

The LQZJ-0.66 designation follows the GB/JB Chinese instrument-transformer naming convention. Each character encodes a specific construction or rating attribute:

2.2 Standard Variant Matrix

The LQZJ-0.66 is offered in multiple electrical configurations, each defined by primary current, accuracy class, and rated output. All variants share the same mechanical envelope and Ø103 mm aperture, allowing a single switchgear cutout to accept any electrical specification.

2.3 Series Evolution

The LQZJ-0.66 supersedes the legacy LQG-0.5 series introduced in earlier GB design generations. Mechanical envelope, mounting interface, and primary aperture (Ø103 mm) are fully backward-compatible. Engineering improvements over the predecessor include: upgraded epoxy resin formulation with improved thermal endurance and reduced partial-discharge inception voltage variability; refined core grain orientation for lower magnetising current at low primary excitation; and tighter accuracy banding across the 25–120% I₁n metering range.

3. Service Conditions

The LQZJ-0.66 is qualified for indoor service per IEC 61869-1 clause 4 normal service conditions. Operation outside the limits below requires engineering review and may necessitate derating, alternative insulation class, or special configuration.

4. Construction

4.1 Construction Design

Magnetic core

Toroidal (ring-type) wound from grain-oriented silicon steel (CRGO, typically 0.30 mm or 0.27 mm thickness). Core annealed after winding to relieve mechanical stress and restore magnetic permeability. For low-current ranges (I₁n ≤ 50 A), nickel-iron alloy cores may be specified for improved low-end accuracy.

Primary circuit

Single-turn pass-through configuration. The Ø103 mm aperture accepts a busbar or cable as the primary “winding”. No dedicated primary terminals; the user-supplied conductor passes through the window in the direction marked P1 → P2 on the housing.

Secondary winding

Multi-turn copper magnet wire (Class B or Class F enamel insulation) wound uniformly around the core. Number of secondary turns N₂ equals the rated transformation ratio (e.g., 200/5 → N₂ = 40). Inter-turn insulation and mechanical reinforcement are integrated into the winding assembly before encapsulation.

Insulation system

Vacuum-cast epoxy resin fully encapsulates the core-and-coil assembly. The cast body integrates primary-to-secondary insulation, secondary-to-ground insulation, mechanical support, and environmental protection in a single monolithic structure. Standard thermal class is B (130 °C); class F (155 °C) available on request.

Housing

Flame-retardant thermoplastic outer shell (UL94 V-0) over the cast-resin body, providing mechanical protection during handling and IP20 ingress protection in service.

Mounting base

Integrated polymer base with two interface options: bottom mounting (footprint suitable for panel-floor fixing) or side mounting (suitable for vertical busbar installations). Each base offers either 2-hole or 4-hole fixing patterns; M6 hardware is standard.

Terminals

Secondary terminals S1 and S2 are stud-type (M5 or M6 brass) with locking nuts and washers, located on the front face. Polarity is permanently marked on the housing in compliance with IEC 61869-2 cl. 6.13 (primary P1/P2 corresponds to secondary S1/S2 in subtractive convention).

4.2 Windings & Terminal Marking

Reference current direction: when primary current i₁ enters at P1 and exits at P2, secondary current i₂ flows out of S1, through the external burden, and returns at S2. This subtractive polarity is mandatory for correct kWh metering, watt-metric earth-fault protection, and any directional relay function.

5. Technical Data

This section provides selection-grade electrical data for the LQZJ-0.66 series. All values apply at the rated burden and rated frequency as marked on the nameplate. For configurations outside the standard ranges, technical agreement and a project-specific datasheet shall govern.

5.1 Primary & Secondary Ratings

Note: 1 A secondary configurations available on request; consult factory for non-standard ratios.

5.2 Accuracy Class Limits (per IEC 61869-2)

For class 0.2 and 0.5, accuracy is verified across 25%–100% of rated burden and 5%–120% of rated current. The accuracy limit factor (ALF) for protection class 10P is typically 5, 10, 15, 20, or 30 — specified on the nameplate as e.g. “10P10” (composite error ≤ 10% at 10 × I₁n).

5.3 Thermal & Dynamic Withstand

The short-time thermal current Ith (1 s) and dynamic peak current Idyn are governed by the relations:

For LQZJ-0.66, standard ratings are Ith = 50 × I₁n / 1 s and Idyn = 100 × I₁n peak. Both must equal or exceed the system prospective short-circuit current Ipsc and peak fault current Ipk at the installation point. Verification is by factory short-circuit type-test report referenced on the routine-test certificate.

6. Standards & References

6.1 Applicable Standards

6.2 Routine Tests (Each Unit)

Performed on every manufactured unit per IEC 61869-2 cl. 7.3 / GB/T 20840.2:

1. Marking verification (P1/P2, S1/S2, nameplate data)
2. Power-frequency withstand voltage test on primary winding (3 kV r.m.s. for 1 minute, 0.66 kV class)
3. Power-frequency withstand voltage test on secondary winding (3 kV r.m.s. for 1 minute)
4. Inter-turn overvoltage test on secondary
5. Determination of errors at rated burden (current error εi and phase displacement δ across 5%–120% I₁n for metering class; composite error at ALF for protection class)
6. Polarity verification (P1–S1 subtractive convention)
7. Insulation resistance ≥ 100 MΩ at 500 V DC

6.3 Type Tests (Design Validation)

Performed on representative samples per IEC 61869-2 cl. 7.2:

1. Temperature rise test at rated continuous current (limits per insulation class)
2. Short-time current test (Ith for 1 s) and dynamic current test (Idyn peak)
3. Lightning impulse withstand voltage test (8 kV peak, 1.2/50 μs, for 0.72 kV Um class)
4. Determination of errors at limit burden conditions
5. Verification of accuracy class extended over the full operating range
6. Mechanical and environmental tests where specified by project

7. Installation & Dimensions

7.1 Outline Dimensions

Refer to the certified dimensional drawing for project-specific tolerances and mounting hole coordinates.

7.2 Installation Guidelines

1. Mount the CT on a clean, flat, rigid surface using all designated fixing holes. Tighten fasteners to manufacturer-recommended torque (typically 6–8 N·m for M6 hardware).
2. Pass the primary conductor (busbar or cable) centrally through the Ø103 mm aperture. Maintain the marked direction P1 → P2 — current flowing in this direction yields S1 → S2 secondary output.
3. Ensure adequate clearance to adjacent live parts per the system insulation coordination (minimum 25 mm air clearance for 0.66 kV class per IEC 60664-1, PD 2).
4. Size secondary wiring to limit total secondary loop resistance such that the burden remains within Sn at rated current. For 5 A secondary, 2.5 mm² copper for runs up to 25 m is typical; longer runs may require 4 mm² or upgrading to 1 A secondary.
5. Connect S1 to the ammeter / meter / relay live input; connect S2 to the instrumentation neutral. Earth one point of the secondary circuit (typically at the protection panel terminal block) — never multiple points.
6. Verify polarity and ratio at commissioning using primary injection or polarity tester before energising the primary circuit.

7.3 Safety & Maintenance Notes

• Always short-circuit S1–S2 before disconnecting downstream instrumentation.
• One point of the secondary loop shall be earthed (typically S2 at the marshalling kiosk).
• The primary conductor shall be installed and supported externally — the LQZJ-0.66 housing is not rated to support primary conductor weight or fault-driven mechanical forces.
• Operating CTs at primary current beyond the nameplate Ith / Idyn ratings during faults will cause permanent magnetic, mechanical, or insulation damage.
• All work shall comply with IEC 60364, GB 26860, NFPA 70E, or the applicable local electrical safety code, including lockout / tagout procedures.

8. Selection Guide (Worked Example)

The following four-step procedure illustrates the selection of an LQZJ-0.66 for a representative application: a 250 A continuous load motor feeder in a 400 V switchboard, with a connected digital multifunction meter and a thermal overload relay, located in a building with 20 m of secondary cable run between the switchboard and the metering kiosk.

Step 1 — Determine rated primary current I₁n

Continuous load current Ic = 250 A. Choose I₁n ≥ 1.2 × Ic = 300 A. Selecting from the standard list: I₁n = 300 A. This places the operating point at 250/300 = 83% of I₁n, well within the 25%–100% optimal accuracy band.

Step 2 — Specify accuracy class

The application requires sub-billing-grade metering — class 0.5 per IEC 61869-2 is appropriate. The thermal relay can share the same metering core in this case (the relay’s accuracy demand of class 1 is automatically satisfied by class 0.5). For a stricter installation, a separate 10P core would be specified.

Step 3 — Calculate required burden

Connected loads on the secondary loop:

• Multifunction meter input: Sm = 0.05 VA (typical electronic)
• Thermal overload relay: Sr = 0.5 VA
• Secondary cable: 20 m × 2 (loop) = 40 m total path; 2.5 mm² copper at ρ = 0.0175 Ω·mm²/m → Rwire = 0.0175 × 40 / 2.5 = 0.28 Ω
• Wire burden Sw = I₂n² × Rwire = 5² × 0.28 = 7.0 VA

Selecting Sn = 10 VA at class 0.5 provides 32% margin, which is sufficient. If the cable run exceeded 30 m, the wire burden would push Sb close to 10 VA — in that case, upsize to 4 mm² cable, or specify 1 A secondary to reduce wire burden by a factor of 25.

Step 4 — Verify short-circuit withstand

System prospective fault current at the switchboard busbar: Ipsc = 25 kA / 1 s. For I₁n = 300 A, the CT’s nameplate Ith = 50 × 300 = 15,000 A = 15 kA / 1 s. This is insufficient. The selected CT must be specified with an enhanced Ith rating (factory option), or the upstream protection clearing time must reduce the equivalent 1-s thermal current to within 15 kA. Recalculating: if breaker clearing time tf = 0.3 s, then Ith,equiv = 25 × √0.3 = 13.7 kA — within the standard rating. Confirm the upstream device’s actual let-through I²t against the CT nameplate.

9. Ordering Information

Each order shall specify the parameters below to enable production release and acceptance. Where the project requires non-standard configuration (extended temperature, alternative thermal class, tropicalisation, special terminal layout, language-specific nameplate), state these explicitly at the enquiry stage; they will be fixed by technical agreement and a project-specific datasheet.

10. FAQs