The NSA3.5 is the Generation 3.5 Transformer Monitoring Unit launched in 2026 by Beijing Aoyi Xinyuan Technology Co., Ltd. (AOYI POWER): a transformer monitoring unit for compact substations. It is AOYI's current model, not a custom model and not a typo for NSA3. The three earlier generations, the NSA6000, NSA2 and NSA3, are discontinued and replaced by the NSA3.5; spare parts and technical service continue for plants already in operation.
1. Where the model name comes from
- NS comes from Nasen: AOYI's predecessor was Beijing Nasen Xinyuan Technology Co., Ltd. A marks the company's first product series.
- The number is the generation: the NSA6000 was the first generation (2011), the NSA2 the second (2012, the industry's first 3-in-1), the NSA3 the third (2014, the industry's first with compact substation cable temperature monitoring), and the NSA3.5 is Generation 3.5 (2026).
- Why 3.5 and not 4: the main improvement in the NSA3.5 is that the wireless cable-joint temperature sensing pioneered by the NSA3 has moved from battery power to passive operation (induction-powered, battery-free), and fiber-ring monitoring and fault recording have been added on the NSA3 hardware platform. That makes it Generation 3.5, and type testing is covered by the NSA3 type test report.
For the story of the 3-in-1, see Origin of the 3-in-1 Transformer Monitoring Unit.
2. Three major upgrades over the NSA3
| Upgrade | NSA3 | NSA3.5 |
|---|---|---|
| Cable-joint temperature | 433 MHz wireless temperature sensing; sensors run on batteries, which drain quickly outdoors in winter cold | Passive wireless temperature sensing: sensors draw power by induction from the cable current, with no batteries and no wiring; 9 sensing points as standard; sensor offline and probe open-circuit are reported separately |
| Fiber ring | Self-healing ring with only front-panel fiber LEDs; a fault was often found only after both fiber paths were down | Fiber-ring monitoring (patented technology): ring closure, the link state of each fiber port and 12 ring alarm types are reported live, and the master station immediately sees which compact substation and which port is affected |
| Fault analysis | SOE event records | Fault recording + trip reports: each trip produces a protection report, and 12 voltage and current channels are recorded from 2 cycles before to 8 cycles after the fault; 8 records are stored and can be exported in COMTRADE format |
Compared with the separate fiber-optic temperature systems common on site, the NSA3.5 needs no extra temperature host and no fibers routed one by one to the cable joints; temperatures are reported together with the monitoring data.
3. Protection and control upgrades
- Coordinated with ride-through: two-stage overvoltage (fast trip at the high setting, slow trip at the low setting) plus undervoltage protection, set clear of the high and low voltage ride-through zones; the manual gives recommended settings for wind, solar and energy storage.
- Accurate primary phase-loss alarm: a blown HV fuse is automatically told apart from a PT failure.
- Four-quadrant energy: import and export active and reactive energy are accumulated separately, so energy-storage charging and discharging are metered correctly.
- Millisecond SOE, plant-wide time sync: digital input changes carry millisecond time stamps, with 256 kept separately.
- Remote-control interlocks: close blocked until faults are reset, remote / local interlock and open / close position check, with trip-failure and control-circuit-break alarms.
- 10 non-electrical protections with selectable names; a Chinese LCD for setting the RS485 address, gateway IP and protection settings on site.
4. Key specifications
| Item | NSA3.5 standard configuration |
|---|---|
| AC inputs | 2 groups; current 5 A / 1 A; voltage 400–800 V direct, 100 V via PT (optional) |
| Digital inputs / outputs | 20 / 27 / 40 digital inputs, AC/DC 220 V; up to 10 digital outputs |
| Protection | Instantaneous overcurrent, three-stage overcurrent, zero-sequence, two-stage overvoltage, undervoltage, overload, primary phase loss, temperature, differential (optional), 10 non-electrical protections |
| Records | 500 events; 256 digital-input changes; 24 trip reports; 8 fault records |
| Communication | 8 RS485 master ports; 4 Ethernet ports; 2 single-fiber ports (SC, 20 km) for the self-healing ring; 433 MHz wireless temperature sensing; IEC 60870-5-104 uplink |
| Power / environment | AC/DC 220 V ±20%; operating temperature −40°C to +70°C |
| Dimensions | 218.84 × 223 mm, 240 mm deep, panel-mounted |
For full specifications and wiring diagrams, see the NSA3.5 Technical Manual on the Downloads page; for the product overview, see Products.
5. FAQ
Is the NSA3.5 a custom model? No. It is a standard product: the technical manual and IEC 104 point table can be downloaded from our website, and each configuration can be customized per project.
Can I still buy the NSA3, NSA2 or NSA6000? These three models are discontinued, so new projects should choose the NSA3.5. Spare parts and technical service continue for older units in plants already in operation.
For selection and quotations, email sales@aoyipower.com or call +86 10 8646 1328.