IN ACTION - Vizimax Grid Solutions-How to increase reliability on...breaker at maximum voltage...
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34 | JULY/AUGUST 2012 Read Our Expanded Digital Magazine: www.electricity-today.com Read Our Expanded Digital Magazine: www.electricity-today.com july/august 2012 | 35 dead tank circuit breaker. e circuit breaker is controlled by a point- on wave controller in order to avoid inrush current and network tran- sients when energizing the power plant from the transmission line side. e circuit breaker controller settings were done remotely using the integrated Web interface accessed via a secured Internet connection (SSL), allowing the remote monitoring of the installation, including al- ternating current (AC) measurements, circuit breaker status and alarms. e web interface provided access to an event log and COMTRADE (common format for transient data exchange for power systems) file captured at each circuit breaker and power transformer operation. e unit used has a 2000 events memory capacity, which includes wave- forms data. Aſter the static and the circuit breaker integration tests were com- pleted, power equipment was energized for further verifications. Sev- eral uncontrolled switche-closing operations were then completed on the high-voltage circuit breaker and Power Transformer. e average inrush current of uncontrolled closing operations on the High-voltage circuit breaker was 1.5 PU, with a maximum of 3.4 PU. To reduce inrush currents with the controlled switching unit, two methods were proposed by Vizimax: Closing the high-voltage circuit breaker at maximum voltage strategy and Closing the high-voltage cir- cuit breaker using the delayed control strategy and taking into account the residual flux of the power transformer. Closing at maximum voltage strategy When the residual flux is unknown or if the circuit breaker is closed before the completion of the residual flux calculations, the controller is designed to close the circuit breaker at the maximum of the line voltage. From an average of 1.5 PU inrush current with uncontrolled switch- ing, the average inrush current was reduced to 0.55 PU using this closing strategy, which is an improvement of 250 percent over uncon- TODAY’S ELECTRICITY | Get Your Gear On How to increase reliability on transmission networks Figure 1: Step-up high-voltage power transformer and circuit breaker at the Upper Bear Creek Hydro Project SMART GRID SOLUTIONS IN ACTION e proliferation of renewable and hydroelectric power plants inter- connected to transmission lines requires electric utilities and indepen- dent power producers to protect themselves from electrical disturbances that can occur at the end or at sensitive parts of transmission networks due to current inrush while re-energizing power transformers. Traditionally, insertion resistors have been used to mitigate the ef- fect of inrush currents. Yet, a dependable and affordable cost alterna- tive to insertion resistors is the use of point on wave (POW) circuit breaker controllers that calculate and take into account the residual flux of power transformers while they are de-energized. GEAR IN ACTION PROJECT: Upper Bear Creek Hydro Project GEAR USED: Point-on wave circuit breaker controllers MAJOR PLAYERS: Prime Engineering (onsite), Vizimax (support) TAIL OF THE TAPE e Upper Bear Creek Hydro Project, near Sechelt in British Co- lumbia and owned by Ontario-based Regional Power, provides a total capacity of 20 megawatts (MW) needed to interconnect to a 138 kilo- volt (KV) transmission line owned by BC Hydro. BC Hydro requires strict technical specifications about intercon- necting to its transmission network to ensure that BC Hydro and the power production site remain grid code compliant aſter interconnec- tion. is is why Regional Power needed to eliminate disturbances on the BC Hydro transmission Line with seamless power interconnection equipment. Furthermore, Regional Power wanted to protect its high- voltage power assets against current inrushes and over voltages that can occur at each operation on its high-voltage circuit breaker. To that effect, Regional Power has been using a controlled switching unit for a high-voltage circuit breaker since mid-May 2012 to com- pletely eliminate the inrush current while reenergizing their power transformer (see Figure 1) and to keep the power quality of the BC Hydro transmission line intact, which has been a success thus far. Previously in an uncontrolled mode, the re-energization of the power transformer resulted in a maximum inrush current of 3.4 PU (multiple of full load current), as shown in Figure 2 in our digital edition of Elec- tricity Today Magazine. e circuit breaker commissioning started at the end of March 2012 with Prime Engineering onsite and with the remote support of Vizimax. e power plant commissioning ended in May 2012. is Upper Bear Creek facility is equipped with a 16MVA/138 kV power transformer interconnected to the BC Hydro network using a BY PIERRE TAILLEFER, Vizimax Figure 2: Inrush current before and after the commissioning of the controlled switching unit with real-time residual flux calculation Figure 3: Substation Design Drawing at the Upper Bear Creek Facility METHOD 1: Table 1: Current Inrush using method 1 (Closing at maximum voltage strategy)
Transcript of IN ACTION - Vizimax Grid Solutions-How to increase reliability on...breaker at maximum voltage...
34 | july/august 2012 Read Our Expanded Digital Magazine: www.electricity-today.com Read Our Expanded Digital Magazine: www.electricity-today.com july/august 2012 | 35
dead tank circuit breaker. The circuit breaker is controlled by a point-on wave controller in order to avoid inrush current and network tran-sients when energizing the power plant from the transmission line side.
The circuit breaker controller settings were done remotely using the integrated Web interface accessed via a secured Internet connection (SSL), allowing the remote monitoring of the installation, including al-ternating current (AC) measurements, circuit breaker status and alarms.
The web interface provided access to an event log and COMTRADE (common format for transient data exchange for power systems) file captured at each circuit breaker and power transformer operation. The unit used has a 2000 events memory capacity, which includes wave-forms data.
After the static and the circuit breaker integration tests were com-pleted, power equipment was energized for further verifications. Sev-eral uncontrolled switche-closing operations were then completed on the high-voltage circuit breaker and Power Transformer. The average inrush current of uncontrolled closing operations on the High-voltage circuit breaker was 1.5 PU, with a maximum of 3.4 PU.
To reduce inrush currents with the controlled switching unit, two methods were proposed by Vizimax: Closing the high-voltage circuit breaker at maximum voltage strategy and Closing the high-voltage cir-cuit breaker using the delayed control strategy and taking into account the residual flux of the power transformer.
Closing at maximum voltage strategyWhen the residual flux is unknown or if the circuit breaker is closed
before the completion of the residual flux calculations, the controller is designed to close the circuit breaker at the maximum of the line voltage.
From an average of 1.5 PU inrush current with uncontrolled switch-ing, the average inrush current was reduced to 0.55 PU using this closing strategy, which is an improvement of 250 percent over uncon-
TODAY’S ELECTRICITY | Get Your Gear On
How to increase reliability on transmission networks
Figure 1: Step-up high-voltage power transformer and circuit breaker at the Upper Bear Creek Hydro Project
SMART GRID
SOLUTIONS IN ACTION
The proliferation of renewable and hydroelectric power plants inter-connected to transmission lines requires electric utilities and indepen-dent power producers to protect themselves from electrical disturbances that can occur at the end or at sensitive parts of transmission networks due to current inrush while re-energizing power transformers.
Traditionally, insertion resistors have been used to mitigate the ef-fect of inrush currents. Yet, a dependable and affordable cost alterna-tive to insertion resistors is the use of point on wave (POW) circuit breaker controllers that calculate and take into account the residual flux of power transformers while they are de-energized.
GEAR IN ACTIONPROJECT: Upper Bear Creek Hydro ProjectGEAR USED: Point-on wave circuit breaker controllersMAJOR PLAYERS: Prime Engineering (onsite), Vizimax (support)
TAIL OF THE TAPEThe Upper Bear Creek Hydro Project, near Sechelt in British Co-
lumbia and owned by Ontario-based Regional Power, provides a total capacity of 20 megawatts (MW) needed to interconnect to a 138 kilo-volt (KV) transmission line owned by BC Hydro.
BC Hydro requires strict technical specifications about intercon-necting to its transmission network to ensure that BC Hydro and the power production site remain grid code compliant after interconnec-tion. This is why Regional Power needed to eliminate disturbances on the BC Hydro transmission Line with seamless power interconnection equipment. Furthermore, Regional Power wanted to protect its high-voltage power assets against current inrushes and over voltages that can occur at each operation on its high-voltage circuit breaker.
To that effect, Regional Power has been using a controlled switching unit for a high-voltage circuit breaker since mid-May 2012 to com-pletely eliminate the inrush current while reenergizing their power transformer (see Figure 1) and to keep the power quality of the BC Hydro transmission line intact, which has been a success thus far. Previously in an uncontrolled mode, the re-energization of the power transformer resulted in a maximum inrush current of 3.4 PU (multiple of full load current), as shown in Figure 2 in our digital edition of Elec-tricity Today Magazine.
The circuit breaker commissioning started at the end of March 2012 with Prime Engineering onsite and with the remote support of Vizimax. The power plant commissioning ended in May 2012.
This Upper Bear Creek facility is equipped with a 16MVA/138 kV power transformer interconnected to the BC Hydro network using a
BY PIERRE TAILLEFER, Vizimax
Figure 2: Inrush current before and after the commissioning of the controlled switching unit with real-time residual flux calculation
Figure 3: Substation Design Drawing at the Upper Bear Creek Facility
METHOD 1:
Table 1: Current Inrush using method 1 (Closing at maximum voltage strategy)
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36 | july/august 2012 Read Our Expanded Digital Magazine: www.electricity-today.com
trolled switching. The maximum inrush cur-rent for these tests was 1.4 PU, in comparison to 3.4PU using uncontrolled switching.
Closing using the delayed control strategy The used point-on wave controller normal-
ly uses the delayed control strategy that closes the first phase with the highest residual flux first at an electrical target angle correspond-ing to that flux and closing the other phases simultaneously four and a half cycles later.
This strategy resulted in the complete elim-ination of inrush current (0.035 PU). As il-lustrated below in Table 2, comparable results were obtained in the four last operations of the circuit breaker:
PROSThe use of controlled switching units that
calculate and take into account the residual flux of power transformers while they are re-energized has several benefits for BC Hydro and Regional Power, as shown below:
1. Reduction (if not elimination) of in-rush current on high-voltage circuit
breaker operations lowering network outages,
2. Lower voltage disturbances and stress on the transmission line and
on the power equipment to increase the qual-ity of services to customers,
3. Lower maintenance costs of high-voltage power equipment, and;
4. Lifespan extension of high power power equipment, including circuit
breakers and power transformers.
CONSTo be able to take advantage of the use of
controlled switching units that calculate and take into account the residual flux of power transformers, the production site requires the use of the following:
1. High-voltage circuit breakers with speed and repetitiveness, and
2. Independent-pole-operated high-voltage circuit breakers.
LAST LOOK
The commissioning of the Upper Bear Creek installation illustrates the elimination of inrush current when energizing the un-loaded power transformer using a controlled switching unit. The commissioning was done successfully by the onsite system engineer sup-ported by the Vizimax team using a remote secured Internet connection to the controlled switching unit.
The method of closing using the delayed control strategy proved to be the most appro-priate, since inrush current has now been com-pletely eliminated preserving power quality by increasing the stability and the reliability of the transmission line.
WHO TO CALL: Vizimax specializes in point of wave circuit breakers. Check out www.vizimax.com for more information.
COMMENTS: [email protected]
METHOD 2:
Table 2: Current Inrush using Method 2 (Closing using the delayed control strategy)
