Technical Parameters

Service Conditions

• Installation: Outdoor (substations/industrial sites/primary metering points)
• Altitude: ≤1000 m standard; higher altitude on request
• Temperature: Per GB outdoor oil-immersed limits; extremes to be specified
• Humidity: Outdoor moisture-proof/breather protected
• Site condition: Non-corrosive, non-explosive, low vibration/impact
• Lightning: ZnO arrester required within 1 m of the unit

Technical Parameters

The JLSW3-10 is a 10 kV class outdoor oil-immersed three-phase combined instrument transformer for 50/60 Hz AC systems. It features electromagnetic CTs and single-phase PTs in Y/Y connection, with customizable transformation ratios, accuracy classes up to 0.2/0.2S, and compliance with GB 20840 series standards. Designed for altitudes up to 1000 m and standard outdoor temperature ranges per GB specifications.

Model Variants

Frequently Asked Questions

Q1: Are higher accuracy classes available for revenue billing meters?

Yes, the JLSW3-10 provides accuracy classes up to 0.2/0.2S for precise metering. It utilizes electromagnetic CTs and Y/Y connected PTs. Specify your exact transformation ratios during ordering.

Q2: How should this outdoor transformer be protected against lightning surges?

A ZnO surge arrester must be installed within 1 meter of the unit. The transformer itself is moisture-proof and breather-protected for outdoor humidity. Verify site grounding requirements with our engineering team.

Q3: Can the JLSW3-10 operate at altitudes above 1000 meters?

Standard models are rated for altitudes up to 1000 meters. Higher altitude configurations are available upon request. Please provide your exact site elevation for factory verification.

Q4: What factory tests are performed before shipping the JLSW3-10?

Routine tests are conducted per GB 20840 series standards. Specific type tests or special factory acceptance tests are subject to confirmation. Contact our sales team for detailed test reports.

Q5: Which international standards does this 10kV combined instrument transformer comply with?

The JLSW3-10 is designed and manufactured in compliance with the GB 20840 series standards. For specific IEC or regional certification requirements, please contact us for details.

Q6: When is the JLSW3-10 preferred for primary metering points?

It is preferred for 10kV outdoor substations and industrial sites requiring 50/60 Hz combined measurement. Ensure the site is non-corrosive, non-explosive, and has low vibration.

Q7: Which model variant is required for a 6kV distribution system?

You must select the JLSW3-6 model for 6kV systems. The JLSW3-10 is strictly rated for 10kV class applications. Both models support 50 Hz and 60 Hz frequencies.

Installation & Wiring

Outline Dimensions

The outline dimensions and mounting details for the JLSW3-10 10kV outdoor oil-immersed combined instrument transformer are provided in the dimensional drawing above. Ensure sufficient space is allocated during installation to accommodate the unit’s physical size and to allow for proper clearances.

Selection & FAQs

Selection Guide

• Specify system voltage class (6 kV or 10 kV) according to local grid requirements.
• Define PT and CT transformation ratios for accurate three-phase metering and protection.
• Select appropriate accuracy class (0.2 or 0.2S for metering; protection cores if needed) per project specifications.
• Confirm rated burden (VA) for both PT and CT secondary windings to match connected instrumentation.
• Provide operating environment details including altitude, temperature range, humidity, and pollution level for proper insulation rating.
• Indicate any customization needs such as special ratios, high-precision versions, or integration with energy meters at the ordering stage.

Frequently Asked Questions

Q1: How do I correctly select the CT and PT transformation ratios and accuracy classes for revenue metering in a 10 kV outdoor substation using the JLSW3-10?

For revenue-grade metering per GB/T 20840.2–2014 and GB/T 20840.3–2013, specify CT accuracy class 0.2S (not just 0.2) to ensure high precision at low load currents (e.g., 1%–120% of rated current). The PT accuracy should be 0.2 for voltage measurement. Select CT ratios based on maximum expected load current (e.g., 600/5 A for a 10 MVA feeder at 10 kV ≈ 577 A), ensuring the connected meter burden (typically 2.5–10 VA) does not exceed the transformer’s rated secondary burden. Over-sizing the ratio reduces accuracy at light loads; under-sizing risks saturation during faults. Always validate burden compatibility using IEC 61869-2/-3 calculation methods.

Q2: What are the critical installation precautions to avoid common field failures with the JLSW3-10 in outdoor 10 kV distribution systems?

Three key precautions must be observed: (1) Install a zinc oxide surge arrester within 1 meter of the unit—per GB 20840.4-2015 Section 6.4—to limit lightning-induced overvoltages that can degrade oil insulation; (2) Never leave CT secondary windings open-circuited during operation or testing, as this induces dangerous overvoltages (> kV levels) and core saturation; always short-circuit and ground before disconnecting meters; (3) Ensure proper grounding of the tank, base plate, and PT neutral point to prevent floating potentials. Additionally, verify adequate clearance from grounded structures per local switchgear standards (typically ≥125 mm phase-to-ground for 10 kV).

Q3: How does the JLSW3-10 compare technically to separate oil-immersed CTs and PTs or resin-cast combined units in terms of performance and lifecycle cost?

Compared to separate units, the JLSW3-10 reduces footprint by ~40% and eliminates interconnection errors, while maintaining identical electromagnetic performance due to its three independent single-phase PTs and CTs. Versus resin-cast combined transformers (e.g., JLSZV-type), the oil-immersed design offers superior thermal stability (oil dissipates heat more effectively than epoxy), higher short-circuit withstand capability, and better long-term dielectric integrity in humid environments—critical for outdoor substations in coastal or tropical regions. However, it requires periodic oil-level checks and is heavier. Lifecycle cost favors JLSW3-10 in applications >15 years due to lower degradation rates in oil versus UV-exposed resin.

Q4: What is the practical significance of the “rated burden” parameter for both CT and PT secondaries, and how does undersizing affect metering accuracy?

Rated burden (in VA) defines the maximum load the secondary winding can drive while maintaining specified accuracy. For CTs, exceeding burden increases impedance, causing ratio and phase errors—especially critical for 0.2S class where error must stay within ±0.2% at 20%–120% In. For PTs, excessive burden causes voltage drop, leading to under-registration in kWh meters. Example: A PT rated for 30 VA burden connected to a 40 VA load may exhibit >0.5% error, violating revenue metering requirements. Always sum burdens of all connected devices (meters, relays, leads) and include wiring resistance (R = ρL/A). Use 4 mm² Cu conductors for runs >10 m to minimize lead burden.

Q5: Can the JLSW3-10 be deployed at altitudes above 1000 m, and what derating or modifications are required?

Yes, but standard units are rated only for ≤1000 m altitude per GB 20840.1–2010. Above 1000 m, air density decreases, reducing external insulation strength. For installations at 2000–3000 m, request factory-modified units with increased creepage distance (≥20 mm/kV vs. standard 16 mm/kV) and adjusted oil expansion volume to compensate for lower atmospheric pressure. Internal oil insulation remains unaffected, but external clearances must comply with IEC 60071-2 altitude correction factors (k = 1 + (H−1000)/8150). Failure to derate may cause flashovers during switching surges.

Q6: What maintenance procedures and diagnostic tests are recommended to ensure long-term reliability of the JLSW3-10 in harsh outdoor environments?

Perform annual inspections: (1) Check oil level via sight gauge—top up only with filtered, dry transformer oil meeting GB 2536 if below minimum; (2) Inspect the moisture-prevention breather for silica gel discoloration (pink = saturated); replace if needed; (3) Verify tightness of terminal bolts and grounding continuity (<0.1 Ω resistance); (4) Clean porcelain bushings to prevent tracking in polluted areas. Every 5 years, conduct dissolved gas analysis (DGA) if operational anomalies occur—look for H₂, CH₄, or C₂H₂ indicating partial discharge or overheating. Do not perform routine oil sampling unless suspecting internal fault, as breather systems are sealed.

Q7: How does customization of transformation ratios impact lead time and cost, and what alternatives exist for urgent projects?

Standard JLSW3-10 units with common ratios (e.g., 10/√3/0.1/√3 kV PT; 400/5 or 600/5 A CT) typically ship in 4–6 weeks. Custom ratios (e.g., 10.5/√3 kV or 800/1 A) require new winding designs and extended testing, adding 2–3 weeks and ~15–25% cost premium. For urgent deployments, consider stocking standard-ratio units and using external matching transformers (e.g., auxiliary CTs)—though this compromises accuracy and voids 0.2S compliance. Alternatively, verify if nearby JLSW3-6 (6 kV) inventory can be adapted if system voltage tolerates ±5% variation, though this is not recommended for revenue metering.

Q8: Why is Y/Y connection used for the PTs in the JLSW3-10, and what are the implications for grounding and zero-sequence monitoring?

The Y/Y connection provides phase-to-ground voltage measurement essential for three-phase four-wire metering and ground-fault detection in solidly grounded or low-resistance grounded 10 kV systems. However, unlike open-delta configurations, Y/Y cannot inherently measure zero-sequence voltage. For ground-fault protection, an external zero-sequence CT is required on the neutral conductor. Crucially, the PT neutral must be solidly grounded at the transformer base to prevent ferroresonance—a risk in isolated-neutral systems with cable capacitance. This grounding also stabilizes secondary voltage during unbalanced loading, ensuring metering accuracy per GB 20840.3–2013 Clause 5.3.2.