IEEE Transformer Committee PC57.167 Distribution

Transformer Monitoring - User Mark Scarborough

Electrical Engineering Consultant – DuPont

January 9, 2019

Transformer Types in DuPont

• Control power • Dry-type in MCCs and control panels

• Small dry-type • Lighting, receptacle, instrument

power panel type • 5kVA – 330kVA (1 phase and 3 phase)

• Specialty • Dry-type and fluid filled for rectifier

and ASD applications

• Pole top • Small power

• Some 20 – 45MVA main substation transformers

• Distribution (substation) dry-type • VPI conventional wound and cast coil • 750kVA – 3000kVA

• Distribution (substation) fluid filled • Mineral oil, natural ester, silicone

insulation fluids • 750kVA – 5000kVA (some 10MVA and

30MVA)

• Pad-mounted • Mineral oil and natural ester fluids • 100kVA – 3000kVA

Typical Distribution System • Incoming power

• Purchased power substations • Mostly all owned by Utilities • 230kV down to 12.47kV

• Internal plant distribution • Typically medium voltage (1 – 35kV) but

mostly 2.4kV to 13.8KV. Few 34.5kV system.

• Utilization • 480V and 575V for most applications • 2.4kV and 4.16kV for motor applications

about 250HP and above • 120V / 230V for small loads

• Grounding • B-Phase • HGR • LRG • Soild

Transformer Monitoring Techniques

• Control power, small dry-type, pole top • Usually don’t do anything. Investigate when something doesn’t

work or power goes out. • Some pole tops and small dry-types may get an infrared

inspection.

• Visual • Probably the most common but questionable as to what people

know what to look for. • Some plants require an operator or maintenance technician to

walk the main electrical system from substation to substation daily, weekly, or monthly.

• Looking for abnormal sounds and or smells, leaks, broken gages, deterioration in paint system.

• Infrared Inspection • Typically on an annual basis for most facilities. • Good way to see if cooling system is working or if low fluid level.

Transformer Monitoring Techniques • If transformers are fluid filled, then

very good at taking samples for oil screen and DGA on an annual basis. • Typical issues with sample methods and

labs and reporting and interpretation. • Need to realize that you have to put

some oil back in occasionally.

• If critical application, will shut down on a 2 or 4 year interval to do inspection, testing, and cleaning.

• Planned shutdowns sometimes are impossible until the system shuts down automatically.

Transformer Monitoring Techniques – Internal Specification • Three (3) internal standards / guidelines

• Fluid Filled – 300kVA to 10MVA, 3 Ph, primary voltage 2,400 to 46,000V

• Dry-Type – 300 to 7.5MVA, 3 Ph, primary voltage 2,400 to 34,500V

• Pad Mount – 2500kVA and below, primary voltage of 34,500V and below and a secondary voltage of 600V and below

• Each standard describes the feature sets required on each transformer type. User can add or take away as necessary for their application.

Transformer Monitoring Techniques – Fluid Filled • Standard

• Field Dial thermometer with alarm and control contacts.

• Pressure / vacuum gage. • Pressure relief valve. • Large pressure relief device with

alarm contacts (sometimes directional shield).

• Magnetic liquid level gauge with alarm contacts.

• Optional / Custom • Push to test circuit and/or current

monitoring (4-20mA signal) of space heater circuit in ATCs or control box. Space heater control? Thermostat or no thermostat?

• Fan controls and aux contacts off of fan starter and/or control switch.

• N2 bottle monitoring system with alarms.

• Sudden or fault pressure relay with trip and alarm contacts.

• Winding hot-spot temperature indicator relay with alarm contacts.

• Add alarm contacts to pressure / vacuum gage.

• Infrared view ports on ATC.

Transformer Monitoring Techniques – Dry-Type • Standard

• Winding temperature with 3-phase hot spot temperature indication with peak indicator, contacts for alarm, trip and fan control and fan exerciser. (Typically this is a self contained package from the vendor.)

• Infrared view ports.

• Cooling fans w/ running status

• Optional / Custom • Push to test circuit and/or current

monitoring (4-20mA signal) of space heater circuit in ATCs or control box. Space heater control? Thermostat or no thermostat?

• Infrared view ports on ATC.

Transformer Monitoring Techniques – Pad- Mounted • Standard

• Liquid level gauge on 500kVA and above.

• Dial type thermometer with “peak” indicator on 500kVA and above.

• Vacuum / pressure gage on 500kVA and above.

• Pressure relief device.

• Large pressure relief device with alarm contacts on 1000kVA and above.

• Optional / Custom • Require that sample valve be

accessible outside of the HV and LV compartments.

• Require that all gages be accessible outside of the HV and LV compartments.

• Infrared view ports on HV and LV compartments.

• Alarm contacts on liquid level gage, liquid thermometer, and vacuum / pressure gages.

Alarm and Trip Contacts?

• In most cases, these transformers are located in an industrial facility and feed a substation or electrical room that has local DCS / PLC (control system) I/O.

• Historically, some or all of the alarm contacts would be hard wired to local DCS / PLC I/O cabinets. If it didn’t exist, then it basically didn’t get wired any where.

• More recently ……

Alarm and Trip Contacts?

• …. we have been using the I/O capabilities on microprocessor based protective relaying and even expansion I/O modules for such devices.

Example #1

• 13.8kV Metal Clad Switchgear

• Radial feed to 2500kVA transformer but looped to additional substations.

• Switched breaker local to each substation.

• Microprocessor relay local to substation not capable of handling I/O from transformer so wired to DCS local I/O.

Construction Interconnection Dwg

Example #2

• 12.47kV Metal Clad Switchgear

• Radial feed to 1000kVA substation transformer near by.

• SEL-787 protective relay for transformer with differential.

Construction Interconnection Dwg

MV Switchgear Vendor Schematic

Transformer – Vendor Drawing

Example #3

Signals and What Action?

• So now we have gotten the signals to the plant DCS or PLC system.

• A DCS screen or HMI screen is developed with the alarm points.

• DCS / PLC system is monitored by Operation / Operations. Sometimes they don’t know how to respond.

• Started developing action / resolution matrix. • Call the on call maintenance electrician? • Go to field and look at the equipment? • System automatically send Text message to on call maintenance electrician

response? • Shutdown the process so the transformer can be shutdown?

• Alarms can go into a PI Data Historian system but not aware of active trending.

Misc. Topics / Considerations

• Confusion as to what to do with an alarm comes in. What action is required?

• Firewalls and cyber security. • Not all sites have a centralized DCS or PLC to connect to. • Typically do not monitor of pad mounted transformer but we have some

that are in critical applications. • Been some interest in:

• On line monitoring for moisture. (On line moisture removal systems in service.) • On line monitoring for DGA monitoring. • Better monitoring of dry-type transformers. Have had some sudden failures. • Starting to experiment with wireless communications technology for instruments.

Thinking may be able to use for transformers because not part of process control. • Trending / data collection.

Thank You.

• Questions / Discussion