Bushing and problem-detection monitor: bushings, OLTC, cooling, partial discharge and multi-gas DGA on a single platform
Anticipating bushing failure on a high-voltage transformer — up to 50% of those failures end in a fire — means measuring bushing capacitance and power factor online, at operating voltage and temperature, not only in an offline test every few years. The C50 does this with sensors on each bushing test tap, using the sum of currents method (up to 6 sensors per card, two sets of bushings) or the voltage reference method (3 sensors and 3 reference voltages), and on the same platform it monitors the on-load tap changer, cooling and partial discharge, integrates third-party multigas DGA and moisture analysers and can take over voltage control. It operates from -40 to +70°C.
C50 key data
- Bushings: the C50 continuously measures the capacitance and power factor of each bushing, by sum of currents with up to 6 sensors (two sets of bushings) or by voltage reference with 3 sensors and 3 VT reference voltages; expandable to 12 inputs, with temperature correlation.
- On-load tap changer: motor current and voltage, operation counter per tap position, contact wear per tap, Delta T, slow tap change alarm, reversing switch alarm and breather.
- Cooling: fail-safe control through form C relays for more than two stages, dual-speed fans, parallel pumps with equal-wear duty cycling and a VSD output; monitors fan and pump current, contactor status and oil flow.
- Thermal model: hot spot adjusted to the transformer design, the losses of each tap position and cooling system health, or measured with a fibre optic probe; insulation ageing and active moisture modelling.
- Dissolved gas and partial discharge: serial-link integration of third-party multigas DGA and moisture analysers, preserving digital precision; partial discharge module connected to the bushing test taps, with synchronised measurement across all channels.
- Voltage control: primary or backup, with line drop compensation using R and X, definite or inverse time delay, and paralleling by circulating current, reverse reactance or master-follower over fibre.
- Architecture and communications: mandatory CPU, communications and power supply modules plus I/O cards in a C54 (4 cards) or C59 (9 cards) frame; 10/100 copper and fibre Ethernet with built-in switch, 2 RS-485 and one optional RS-485, RS-232 or serial fibre port; DNP3, Modbus and IEC 61850.
- Power and mounting: 110-240 VDC or 110-250 VAC (50-60 Hz), 48 VDC on request; -40 to +70°C; control unit on DIN rail or panel, interface unit also in a 19" rack.
Advantages
Real-time bushing monitoring
50% of bushing failures end in fire. The C50 provides real-time bushing data in any weather condition, load and rated voltage, with the sensitivity of an offline measurement.
Two bushing measurement techniques
Sum of currents detects leakage-current imbalance between bushings; voltage reference calculates each bushing's power factor independently and is less affected by grid fluctuations.
Integrated partial discharge and dissolved gas
Measures up to 15 electrical partial-discharge channels with tap sensors, RFCTs and Rogowski coils, and integrates third-party multi-gas DGA and moisture analysers over a serial link.
OLTC and cooling diagnostics
Monitors tap position and the tap-changer motor current and voltage, and tracks fan and pump current, contactor status and oil flow for the cooling system.
Applications
- High-voltage transformers with bushings rated 69 kV and above.
- Condition-based maintenance of bushings, OLTC and cooling system.
- Consolidating third-party data — multi-gas DGA, moisture — on one platform.
- Fire prevention through early detection of bushing deterioration.
About the product
The C50 integrates into a transformer monitoring platform that consolidates bushing, temperature, OLTC, cooling and partial-discharge data in one place, along with third-party devices such as multi-gas DGA analysers. The built-in web dashboard lets users view the data from any browser, with no software installation.
Bushing monitoring combines sensors installed in each bushing's capacitance tap with a balancing unit and a summation unit: under balanced conditions the vector sum of leakage currents is zero, and a change in a bushing's capacitance or power factor produces a deviation whose magnitude indicates severity and whose vector points to the affected bushing. The unit learns normal behaviour with load, humidity and temperature.
Available accessories: BAU bushing sensors; 8, 16 and 28 kV coupling capacitors for bushings without a capacitance tap; Rogowski coils and radio-frequency current transformers; a contact wear sensor kit for the OLTC; and a switching kiosk for installations with a spare single-phase transformer.
Technical specifications
| Thermal monitoring | Top oil, ambient and load; calculated hot spot; thermal ageing |
| Bushings | Up to 6 BAU sensors; sum of currents or voltage reference; power factor and capacitance |
| Partial discharge | Up to 15 electrical channels; tap sensors, RFCTs and Rogowski coils |
| Dissolved gas and moisture | Serial integration of third-party multi-gas DGA and moisture analysers |
| OLTC | Tap position, motor current and voltage, Delta T; optional contact wear sensor |
| Cooling | Staged control; fan/pump current, contactor and oil-flow monitoring |
| Voltage control and fibre optics | Essential tap-changer voltage control; optional winding fibre-optic probe |
| Communications | DNP3, Modbus, IEC 61850; copper/fibre Ethernet, RS-232/RS-485; web dashboard |
| Power supply and mounting | 110-240 VDC or 110-250 VAC; -40°C to +70°C; DIN rail, panel or 19″ rack |
| Frame | C54: up to 4 expansion cards · C59: up to 9 expansion cards |
| Annunciator inputs | 30-276 VAC or 15-390 VDC, with self-resetting overcurrent protection and overvoltage protection |
| Serial ports | 2 RS-485 plus 1 optional RS-485, RS-232 or serial fibre; simultaneous master or slave operation |
Frequently asked questions
Which bushing monitoring method is better, sum of currents or voltage reference?
The C50 supports both. Sum of currents connects up to 6 sensors for two sets of bushings: in a balanced system the vector sum of the leakage currents is zero, the size of any deviation shows the severity and its vector points to the affected bushing. Voltage reference connects 3 sensors on one set of bushings plus 3 VT reference voltages and calculates the power factor of each bushing independently, being less sensitive to network fluctuations.
Can the C50 monitor bushings without a test tap?
Yes. For bushings without a test tap, an 8, 16 or 28 kV coupling capacitor is used, which allows the same capacitance and power factor measurement as the tap sensor.
How many bushings can the C50 monitor?
Up to six, with BAU sensors and either the sum-of-currents or voltage-reference technique.
Does it detect partial discharge?
Yes, up to 15 electrical channels with tap sensors, RFCTs and Rogowski coils.
Does it integrate dissolved-gas analysis?
Yes, via a serial link to third-party multi-gas DGA and moisture analysers.
What does it add over a basic temperature monitor?
Bushings, OLTC, partial discharge, multi-gas DGA, essential voltage control, cooling monitoring and fibre optics.
The Dynamic Ratings C50 is manufactured by Dynamic Ratings and distributed by Amperis.
