Überwachungssystem für Verteilungstransformatoren: Parameter, Kommunikation und Einsatz

Veröffentlichungsdatum:2. Oktober 2026, 17:12:31 Uhr

  • What it is: a Transformatorüberwachungssystem is a set of sensors, local controllers, a communication gateway and a data platform that tracks the health of a distribution transformer in real time.
  • Parameters to measure: winding temperature, top oil temperature, load current, oil level and pressure are the baseline. Dissolved gases, partial discharge, bushing condition and tap changer status are added for critical units.
  • Communication: RS485/Modbus RTU for local devices, Modbus TCP, IEC 60870-5-104 or DNP3 to SCADA, and IEC 61850 in digital substations. Local alarm and trip must keep working if the network fails.
  • Deployment: collect nameplate data, choose sensors by transformer type and criticality, route cables away from live parts, verify every channel against a reference, test alarm contacts, then calibrate once a year.
  • Typical configurations: a temperature controller for dry-type units, a winding and oil temperature indicator for standard oil-immersed units, and fiber optic hot spot sensing plus online DGA for critical assets.

Inhaltsverzeichnis

1. Monitoring Parameters for Distribution Transformer Sensors and Transmitters

Transformatorüberwachung – Architektur des Überwachungssystems

Baseline parameter table

Parameter Sensor / Source Typical Sampling Interval Priorität
Winding (hot spot) temperature Fiber optic probe, Pt100 or winding temperature indicator 1–10 s Hoch
Maximale Öltemperatur Oil temperature indicator or Pt100 1–60 s Hoch
Load current and voltage CT / PT or multifunction meter 1 s Hoch
Oil level and pressure Level and pressure transmitters 10–60 s Mittel
Gelöste Gase Online-DGA-Monitor 1–24 h Medium to high
Teilentladung UHF, HFCT or acoustic sensor Continuous Medium to high
Bushing capacitance and tan δ Bushing tap adapter Continuous Mittel
Cabinet temperature and humidity Environmental sensor 1–5 min Niedrig

Scope by transformer type

  • Dry-type (cast resin or VPI): winding temperature per phase, fan status, enclosure temperature and humidity.
  • Oil-immersed, standard: top oil temperature, winding temperature, oil level, load current.
  • Oil-immersed, critical: add fiber optic hot spot sensing, online DGA and bushing monitoring.
  • With on-load tap changer: add tap position, motor current and a gas or moisture sensor in the OLTC compartment.

2. Dry-Type Transformer Temperature Controller and Fan Control

What the controller must do

  • Read three phase sensors: one Pt100 per phase winding, plus an optional core or enclosure channel. A dedicated device such as the IB-S201 Temperaturüberwachungs- und -regelgerät für Trockentransformatoren handles these inputs locally.
  • Drive cooling fans: start and stop fans through a relay with hysteresis so they do not chatter around the setpoint.
  • Provide alarm and trip relays: two independent dry contacts, wired to the protection circuit and not only to SCADA.
  • Offer RS485 output: Modbus RTU registers for temperatures, relay states and sensor-fault flags.
  • Detect sensor faults: open-circuit and short-circuit detection prevents a broken probe from reading as a normal temperature.

Insulation class and temperature reference

Isolationsklasse Maximale Wicklungstemperatur Durchschnittlicher Wicklungsanstieg (IEC 60076-11)
Klasse B 130 °C 80 K
Klasse F 155 °C 100 K
Klasse H 180 °C 125 K

Installation points

  • Insert Pt100 probes into the winding air ducts of the middle section of each LV winding, where the hot spot usually sits.
  • Keep sensor leads away from HV connections and use shielded cable grounded at the controller end only.
  • Check that the controller supply voltage matches the available auxiliary supply (AC 220 V or DC 24–110 V).

3. Oil-Immersed Winding Temperature Indicator and Oil Temperature Indicator

How the two gauges differ

  • Oil temperature indicator (OTI): a capillary or electronic probe in a pocket at the top-oil position that reads top oil temperature directly.
  • Winding temperature indicator (WTI): a thermal-image device. A Anzeige der Wicklungstemperatur adds a heating-element offset, driven by a load current from a CT, to the top oil temperature to estimate hot spot temperature.
  • Limit of the thermal image: the estimate depends on correct CT ratio, heater calibration and gradient data, so it can drift from the real hot spot under changing load.

Parameter comparison

Artikel Oil Temperature Indicator Anzeige der Wicklungstemperatur
Measured value Maximale Öltemperatur Calculated winding hot spot
Typical scale 0–120 °C 0–150 °C
Contacts 2–4 adjustable (fan, alarm, trip) 2–4 adjustable (fan, alarm, trip)
Extra input Keine CT current (typically 0–5 A)
Fernausgang Pt100 or 4–20 mA Pt100 or 4–20 mA

Setup points

  • Fill the OTI pocket with transformer oil so heat transfers properly to the probe.
  • Set the WTI heater current from the transformer test report so the gradient matches the nameplate.
  • Add a 4–20 mA or Pt100 transmitter output when the readings must reach SCADA.

4. Fiber Optic Temperature Sensor and Demodulator for Hot Spot Monitoring

Why fiber optic probes measure the hot spot directly

  • Dielectric probe: the sensing tip has no metal, so it sits against HV windings without creating a discharge path.
  • Störfestigkeit gegenüber elektromagnetischen Störungen: readings stay stable in strong magnetic and electric fields where electrical sensors pick up noise.
  • Direct reading: there is no thermal-model estimate, which matters when overload decisions depend on a few degrees. The principle is explained in more detail in Glasfaser-Temperaturmessung in Transformatoren.

Typical system parameters

Artikel Typischer Wert
Messbereich -40 °C bis 200 °C
Genauigkeit ±1 °C
Reaktionszeit ≤ 1 s
Channels per demodulator 1, 3, 6 oder bis zu 64
Ausgabe RS485 Modbus, 4–20 mA, relay
Probe insulation withstand Suitable for HV winding contact (confirm with datasheet)

Method comparison

Verfahren Maßnahmen EMI-Störfestigkeit Optimale Passform
Pt100 on enclosure or pocket Indirect temperature Moderate Dry-type air or basic oil monitoring
Thermal-image WTI Calculated hot spot High (mechanical) Standard oil-immersed units
Fiber optic probe Direct hot spot Hervorragend Critical or high-load units

Auswahlkriterien

  • Channel count: a 3-channel module covers one three-phase dry-type unit, while a multi-channel demodulator suits several transformers in one substation.
  • Probe type: choose armored probes for oil-immersed windings and polyimide-coated probes for resin or dry-type windings.
  • Extension cable: measure the run from the tank wall or winding exit to the demodulator before ordering.

5. Online DGA Monitor for Critical Distribution Transformers

Was ist die Online-DGA-Überwachung für Transformatoren?

When online DGA is justified

  • The transformer feeds hospitals, data centers, rail traction or process lines where an outage is costly.
  • Periodic oil samples show a rising gas trend, and waiting for the next sampling date is not acceptable.
  • The site is remote or unmanned, so manual sampling is expensive. The trade-offs are covered in Online-DGA-Überwachung von Transformatoren.

Key gases and what they indicate

Gas Typical Fault Indication
Wasserstoff (H₂) Partial discharge, general low-energy fault
Methane (CH₄), Ethane (C₂H₆) Low to medium temperature overheating
Ethylen (C₂H₄) High temperature overheating
Acetylen (C₂H₂) Arcing or very high temperature
CO, CO₂ Cellulose (paper) insulation overheating

Auswahlkriterien

  • Gas coverage: single-gas (H₂ or composite) monitors suit screening, while multi-gas units support Duval triangle and IEC 60599 interpretation.
  • Interpretation basis: use IEEE C57.104 or IEC 60599 limits and watch the rate of gas increase, not only absolute values.
  • Mounting: install on the drain or sampling valve with an isolation valve so the monitor can be serviced without draining the tank.

6. Partial Discharge, Bushing and OLTC Monitoring Devices

Partial discharge sensors

  • UHF sensors on the drain valve detect internal discharge with good noise rejection.
  • HFCT sensors on bushing taps or the ground strap suit retrofit work.
  • Acoustic sensors on the tank help localize the source. A complete overview of methods is in Überwachung von Teilentladungen in Transformatoren.

Überwachung von Buchsen

  • Measured values: capacitance change and dissipation factor (tan δ), compared between phases.
  • Why it matters: bushing insulation faults can lead to tank rupture or fire, so trend-based bushing monitoring is worth adding on high-value units.

OLTC-Überwachung

  • Measured values: tap position, drive motor current or torque, operation counter and temperature difference between the OLTC compartment and the main tank.
  • Typical fault clues: rising motor current, slower operation time and contact wear signs, which OLTC transformer monitoring can trend over time.

7. Communication Gateway, Modbus, IEC 61850 and SCADA Integration

Protocol table

Interface / Protocol Typische Anwendung Mittel Anmerkungen
RS485 / Modbus RTU Controllers and sensors to gateway Shielded twisted pair Up to about 1200 m at 9600 bps
Modbus TCP Gateway to PLC or SCADA Ethernet Simple and widely supported
IEC 60870-5-104 / DNP3 Utility telecontrol Ethernet / IP Common in grid operations
IEC 61850 Digital substations Ethernet Needs ICD/SCD file mapping
4–20 mA / dry contact Legacy RTU and alarm panels Copper Suitable for retrofit projects
4G / 5G / fiber backhaul Remote unmanned sites Wireless / fiber Use VPN and firewall

Data architecture points

  • Protect the local layer: alarm and trip relays must act independently of the network.
  • Standardize tags: use one naming and register map across all transformers, as described in transformer monitoring dashboard and SCADA integration.
  • Synchronize time: use NTP or IRIG-B so events from different devices can be correlated.
  • Secure remote access: role-based accounts, encrypted links and disabled unused ports.

8. Alarm, Trip and Relay Output Settings

Four-stage alarm scheme

Bühne Relay Action Setting Basis
Lüfterstart Start cooling fans Below alarm, per manufacturer
Pre-alarm Notify operator, review load Insulation class and loading guide
Alarm Dispatch inspection, reduce load Nameplate temperature rise
Reise Disconnect the transformer Maximum permissible temperature

Example starting points

Transformatortyp Lüfter starten Alarm Reise
Dry-type Class F winding 100–110 °C 130 °C 150 °C
Dry-type Class H winding 120–130 °C 155 °C 170–180 °C
Oil-immersed top oil 65–75 °C 80–85 °C 95–105 °C

Regeln festlegen

  • Treat the values above as starting points only and confirm every setpoint against the nameplate and manufacturer manual.
  • Base overload permissions on transformer temperature rise limits and IEC 60076-7 or IEEE C57.91 loading guides.
  • Add a 2–5 °C hysteresis to the fan relay to avoid rapid cycling.
  • Record every setpoint change with date, reason and approver.

9. Deployment and Commissioning Checklist for Monitoring Devices

Before installation

  • Collect rating, cooling type, insulation class, temperature rise and test report data.
  • Decide whether the unit is new, where sensors can be embedded, or in service, where only retrofit options exist.
  • Define the sensor list, controller model, gateway and power supply.
  • Confirm the SCADA protocol and register map with the control team.
  • Agree on the outage window and safety clearances.

During installation

  • Route fiber and signal cables away from HV live parts and respect the minimum bend radius.
  • Ground cable shields at one end only.
  • Seal cable glands against moisture, especially on outdoor pad-mount units.
  • Label every channel, cable and terminal to match the drawings.

Commissioning tests

Test Verfahren Bestehenskriterium
Temperature channel check Compare with reference thermometer Im Rahmen der Gerätegenauigkeit
Relay output test Simulate setpoints, check contacts Correct fan, alarm and trip action
Sensor fault test Disconnect probe Fault flag raised
Communication test Read all registers from SCADA Die Werte entsprechen der lokalen Anzeige

Nach der Inbetriebnahme

  • Write a response procedure for each alarm level and train the operators.
  • Store baseline readings at known loads for later comparison.
  • Schedule an annual check of sensors, wiring, contacts and communication.

10. Selection Matrix: Temperature Controller vs Fiber Optic System vs DGA Monitor

Scenario Suggested Configuration Kommunikation
Indoor dry-type, commercial building Temperature controller with fan output RS485 / Modbus RTU
Standard oil-immersed distribution unit WTI and OTI with optional transmitter Dry contact or 4–20 mA
High-load oil-immersed unit Fiber optic hot spot system Modbus TCP / IEC 104
Critical asset feeding sensitive loads Fiber optic, online DGA and bushing monitor IEC 61850 / SCADA
Voltage-regulating unit with OLTC Temperature plus OLTC and DGA monitor Modbus TCP / DNP3

11. FAQ: Distribution Transformer Monitoring System Questions

What does a distribution transformer monitoring system include?

It includes temperature sensors or indicators, a local controller with alarm and fan relays, optional DGA, partial discharge and bushing sensors, a communication gateway and a SCADA or cloud platform.

Which parameters should I monitor first?

Start with winding temperature, top oil temperature and load current. Add oil level, dissolved gases, partial discharge and bushing data when the transformer is critical or high-value.

How does monitoring differ between dry-type and oil-immersed transformers?

Dry-type units focus on winding temperature and fan control because they rely on air cooling. Oil-immersed units add oil temperature, level, pressure and, where justified, DGA.

When should I use a fiber optic temperature sensor instead of a Pt100 or WTI?

Use fiber optic sensing when you need direct hot spot readings, high accuracy and immunity to electromagnetic interference, usually on critical or heavily loaded units. Pt100 and WTI are usually adequate for lightly loaded general-purpose transformers.

Welches Kommunikationsprotokoll soll ich wählen?

Modbus RTU or TCP suits most industrial and commercial projects. Utilities usually use IEC 60870-5-104 or DNP3, and digital substations use IEC 61850. Choose the protocol your control system already supports.

Can I add monitoring to a transformer already in service?

Yes. Oil temperature probes, WTI, current-based load monitoring, online DGA and external PD or bushing sensors can be retrofitted. Embedded winding probes are normally installed during manufacture or major overhaul.

Does every distribution transformer need online DGA?

No. Online DGA is typically kept for critical units. For many distribution transformers, temperature monitoring plus periodic sampling is sufficient, as compared in online DGA vs oil sampling.

How often should the monitoring system be calibrated?

Follow the manufacturer's interval. A common practice is an annual functional check of sensors, alarm contacts and communication, with recalibration if drift is found.

How do I get a configuration for my project?

Prepare the transformer type, rating, cooling method, insulation class and communication requirement, then Leiten Sie diese an das Entwicklerteam weiter for a matched monitoring scheme.