bmt300 - product presentation - v9 april 2013

BMT 300 - Product presentation – v9 - April 2013 - slide 1

Intellix BMT 300

GE Digital Energy Monitoring & Diagnostics

Product Presentation

TM


Bushing failure

Bushings have been identified as the cause of about 15% of all transformer failures

According to Doble, the leading cause of >100MVA transformer failure is bushing failure (35%)

A Western Power survey of 2096 transformer failures in ANZ found that bushing were only second to OLTC as the initially source of failure.

Over 50% of failures are catastrophic, leading to: Total loss of the transformer Environmental issues due to oil release Likely property damage Possible human casualties


Why “on-line” monitoring ?

Periodic testing is simply not enough:

• Periodic testing is not without cost: it takes time, ties up workers and requires an outage

• It is performed at lower voltages (10kV) and under very different temperature conditions (due to absence of load)

• Because of the need for an outage, it is performed at best every year and most likely every 2-5 years

• Most importantly, periodic testing misses quickly progressing (over weeks to months) problems that can arise between tests

On-line bushing monitoring systems can now continuously check for and detect developing faults at an early stage, enabling to plan and schedule an outage for maintenance/replacement and prevent a catastrophic failure from occurring.


Intellix BMT 300

What is it ?

An on-line system that :

• continuously monitors the condition of transformer bushings and

• detects the presence of Partial Discharge (PD) activity in the main transformer tank.

It will alert personnel of developing fault conditions at an early stage and provide vital additional health information on the bushings and the transformer.


How it works

The BMT 300 connects to the 3x HV bushing tapping points using custom made adaptors. Option for both HV and LV bushings (6 bushings).

Using the same adaptor, it measures leakage current , low/power frequency signals (used for BM) and high frequency signals (used for PD).

Additional sensors are used: - Ultra precise GPS timing signal - Ambient temperature & humidity - Top oil temperature - CT on neutral

Uses the same PERCEPTION software (as used by TRANSFIX products) to visualize and analyze the results for:

Bushing status (% change in C1, % change in PF) Presence of Partial Discharge activity


Bushing adaptors tapping point

High frequency current transformer on neutral bushing

Top oil temperature sensor

Ambient temperature sensor

Humidity sensor

BMT 300 – View of an installed unit

Can also connect to 6 bushings: 3 HV + 3 LV

Cable in red is RG58 coax cable


Basic premises:

We, like all other “on-line” systems, work on the assumption that: • The 3 bushings are part of a 3 phase system • The load on all 3 bushings is fairly similar • Phase difference between phases assumed to

be ~120o and consistent • The 3 bushings are very similar • Not two bushings will fail simultaneously

We are therefore looking for the bushing which characteristics are changing significantly compared to the initial install value and more than the other two.

.

How does it work ?


First we calculate what the reference leakage current should be for the baseline C1 value measured when the bushing was installed. We then continuously measure the leakage current of each bushing from the test tap and calculate the % change in current which is the same as the change in capacitance C1.

We then plot the percentage change in C1 value. This is indicative of a loss in dielectric efficiency:

• Nameplate C1 +/-5% - bushing acceptable • Nameplate C1 +/-5% to +/-10% - monitor bushing • Nameplate C1 +/-10% or greater - replace bushing

To make it easier to see the largest change of the 3 and to eliminate load and temperature that affect all 3 bushing, we use a polar plot where we plot the sum of the three vectors, each vector with magnitude equal to the percentage change.

.

Bushing - Capacitance C1

The affected bushing appears clearly, bushing B in this case, with the change in current/capacitance


We measure the time difference when the sine wave of each current phase crosses the origin. This timing difference is converted into a relative angle difference between the phases. In a perfect world, phase B is delayed 120° after phase A and phase C is delayed 240°. Because an increase in PF results in a reduction of the phase delay (negative change in angle), the phase with the most angle difference compared to the others is identified as having the largest relative PF change. We calculate the relative percentage PF difference compared to the original reference PF. This is indicative of a deterioration of the integrity of the insulation: • Up to 150% of nameplate PF - bushing acceptable • From 150% to 200% of nameplate PF - monitor bushing • Above 200% increase in nameplate PF - replace bushing

Bushing – Power Factor PF


Utility value

The high frequency signals associated with Partial Discharge activity in the transformer are detected from the HV bushing adapter.

They are then discriminated against to try and ensure that the PD detected is internal to the transformer and not external (corona discharge).

A final discrimination check can be done manually by comparing PD activity changes with the humidity correlation factor.

Partial Discharge - PD

The system records: • the number of PD events (PD count) - in units • the average amplitude of the PD pulses (PD value) – in pC

It then calculates the Partial Discharge Index (PDI) in mW to represent the average apparent PD power over a pre-defined period.


The big issue with bushing monitoring is avoiding false positives: making sure that we don’t raise an alarm when outside factors affect the bushing parameters that we measure but do not indicate a deterioration of the bushing.

An increase in power being carried will increase the temperature of the oil and the bushing temperature. The leakage current will increase and this must not be mistaken for a change in capacitance.

Outside influence - bushings

Ambient temp. changes (nigh/day) will also have the same influence, due to dimensional changes/expansion. Same for a tap change on transformers with tap changers, which will be change the current.

To avoid this, we:

1. Correlate the change of C1 value relative to the change in temp. of the bushing and relate it to the nameplate C1 always measured at 20oC.

2. Use the polar plot method to display any changes and set the alarms so that any increase seen by all 3 bushing simultaneously is disregarded.


Outside influence - PD

To make sure that we don’t raise false alarm, we will use 3 discrimination methods:

1. Polar plots. Corona will affect all bushing to the same extent and any PD appearing on all 3 bushings equally will be negated.

2. Correlation with humidity. Comparing increases in PD linked to increases in the Humidity correlation factor to detect corona.

3. Pulse Polarity Detection. Comparing the direction of the signals received from the bushing adapters with that of the neutral CT. Same polarity: external, Opposite polarity: internal.

PD being very rapid to develop means that a shutdown is required quickly after it is detected.

Unfortunately, PD can also be generated externally to the transformer through Corona discharge in the environment. This occurs during electrical storms in high humidity environments, especially with rain and wind.


In a polar plot, the measured value for each of the three bushings/phases are shown as vectors at angles 0o (phase A), 120o (phase B), 240o (phase C) .

The magnitudes at a particular time are the percentage difference of the measured value compared to the reference value.

By plotting the vector sum of the three differences on the polar plot, any common cause affecting all 3 bushings will be eliminated and the difference in the affected bushing will appear much more clearly.

Evolution over time is also shown by the darkening of the blue vector colour.

Here clearly there is difference of up to 0.4% compared to nominal for bushing B compared to the others.

Polar plots


Alarms

Alarms

• Alarms can be set for two different warning levels: caution (Hi) and danger (Hi-Hi).

• Alarms can be set on: ‒ Capacitance % change ‒ Power Factor % change ‒ PD Counts ‒ PD value ‒ Partial Discharge Index value ‒ PDI rate of change

• Separate service alarm


Bushing Adaptor & Cable

The Bushing Adapters are all made to measure for each bushing, for: • Physical connection - to make sure we get proper contact • Electrical protection – safety, see next slide

It is important to obtain this information from the customer and to ensure it is correct for all 3 bushings (one may have ben replaced…)

RG58C/U coaxial cable is used (Belden part no: 8262) to connect from each adapter (x3) and from neutral CT to the BMT cabinet. Cable is run in sealed conduit. Cable can be purchased in rolls of 150m (500ft).


Bushing Adaptor Safety

Resistor Resistor GDT GDT

Gas Discharge Tubes (GDT) Redundant Resistors

1) Bushing must be effectively earthed if cable becomes open circuit Redundant resistors in bushing adaptor ensure that tap point has connection to ground at all times and limit voltage in cable to 5V. Unit can detect if one fails

2) Voltage at remote end of cable is always limited By the resistors, in normal operation, to <10V By the two GDTs, in the event of a lightning strike, to <90V for a few micro seconds


User Interface

HMI • Sunlight visible colour LED indicators for

power and the status of the 3 alarm relays

Software • Results can be downloaded and visualized

using GE’s Perception software


Outputs

Digital • Modbus RTU/ASCII protocol over isolated RS-485

Comms Option 1: Fiber Optic • Modbus RTU over serial multimode Fiber Optic (ST

connector) instead of standard output Comms Option 2: Multi-master option • Modbus TCP over Ethernet (RJ-45 connector) or • Modbus TCP over multimode 10Mbps Fiber Optic (ST)

Relays • 3 dry contact relays • Used for warning (Hi), alarm (hi-Hi) and service

Local comms for setup • USB port

Analog Outputs • None


• Communicates to Perception only • No SCADA connectivity (only one master) • Uses pass-through mode in Transfix 1.6

.

RS485

Application 1 - Integrated with Transfix with standard comms

Transfix 1.6 Perception

• DGA data and trending • Bushing data, trending and

polar plots

Note: If need to connect to more than one Master: Perception and something else (like a SCADA system), you must use the Multi-Master option (see next slide).


• Communicates to Perception and SCADA system

• Ethernet connection

RS - 485

.

Perception

LAN

Modbus RTU

Modbus TCP

MULTINET FE Ethernet 10 Mbps

Multinet FE mounted inside BMT 300 enclosure

Application 2 - Integrated with Transfix with comms option 2

RTU/SCADA

Modbus TCP

Modbus TCP


• Fiber Optic connection to LAN (with F.O./RJ45 switch within the LAN)

• Maximum of 3 master stations over Modbus TCP

RS 485

.

PERCEPTION

Modbus RTU

Modbus TCP Modbus TCP Modbus TCP

MULTINET FE

Multinet FE mounted inside BMT 300 enclosure

Application 3 – Multiple users with Communication Option 2

RTU/SCADA 1

RTU/SCADA 2

FIBRE OPTIC

ETHERNET FIBRE OPTIC

LAN

RJ45

Note: only one 10Mbps Ethernet connection at a time to the LAN: Fibre Optic or RJ45

RJ45


Applications

Customers:

• T&D utilities

• Industrials

• Transformer manufacturers

And not just for transformers…

… but for any asset with oil filled bushing that are part of a 3 phase system e.g. CT’s, switches, …


M&D Integrated Solution – Substation Application


BMT 300 – Benefits

Bushing Monitoring • Advance warning of bushing needing

maintenance/replacement • Avoids catastrophic bushing failure and often full

transformer loss • Enables Condition Based Maintenance (CBM)

Partial Discharge Detection • Feature engineered using the same tap adaptor

• Advance warning of possible arcing in main transformer tank

Integration with TRANSFIX multi-gas DGA units • Provides a complete transformer solution to effectively monitor

the majority of root causes of transformer failures. • Uses same PERCEPTION software to visualize data • Less vendors installing equipment in your switchyard

• Single-vendor integrated solution that works/communicates

Questions ?

bmt300 - product presentation - v9 april 2013

Documents

product presentation

bushing failure bushings

intellix bmt

transformer failures

lv bushings

neutral bushing

bushing adaptors

mva transformer failure