WO2000021175A1 - A protective relay-based monitoring system of dc power within an electric power substation - Google Patents
A protective relay-based monitoring system of dc power within an electric power substation Download PDFInfo
- Publication number
- WO2000021175A1 WO2000021175A1 PCT/US1999/023333 US9923333W WO0021175A1 WO 2000021175 A1 WO2000021175 A1 WO 2000021175A1 US 9923333 W US9923333 W US 9923333W WO 0021175 A1 WO0021175 A1 WO 0021175A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- voltage
- ground
- supply
- value
- substation
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/06—Arrangements for supplying operative power
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/16—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass
Definitions
- This invention relates generally to the detection of inadvertent DC (direct current) grounds m the DC supply circuit m an electric power substation, and more particularly concerns a detection system which includes a DC monitoring circuit m protective relays m the substation m combination with voltage information at the contact inputs of the protective relays to determine the location of the DC grounds .
- Power line protection equipment present m an electric power substation will typically include a plurality of protective relays, instrument transformers for converting the values of voltage and current on the line to levels suitable for use m the protective relays, and circuit breakers responsive to the protective relays, as well as other accompanying elements
- the protective relays are used to interrupt AC (alternating current) power distributed from the substation, m response to a protective relay detecting a fault on the power lines.
- Power for the equipment m the substation, including the protective relays is provided by a DC supply system, the source of which is a battery.
- a battery charger is also usually part of the supply system.
- the DC supply system also typically provides power for communication within the substation.
- substation battery systems operate on either 24, 48, 125 or 250 volts DC, although it is common to have two different battery systems m a substation, w th different voltage levels, e.g. one system may operate at 125 volts while the other operates at 48 volts DC
- DC power systems within a substation are operated ungrounded. Grounding of any part of a DC supply system within such a substation would thus typically be unintentional, i.e inadvertent.
- a single inadvertent ground typically will not cause a major DC supply system failure, although it may affect the operation of certain of the equipment within the substation, including possibly the protective relays and the shunt trip coils or close coils which operate the circuit breakers, in particular circumstances.
- a second DC ground in the DC supply system, on the opposing polarity supply bus, will certainly affect the operation of the equipment or blow the fuses in the system.
- a typical DC power system within a substation will include long lengths of wire connections, including wire extending from the battery source in a control house to remote locations in the substation, such as to circuit breakers and system disconnect apparatus. These long wire lengths present significant opportunities for inadvertent DC grounds.
- Inadvertent grounds can occur for a number of different reasons, but typically are due to a breakdown in the wire insulation.
- the damage or breakdown can be due to aging, weather, poor connections or other causes. This can occur in any of the wire runs themselves, whether short or long, even within the control house, or at connections to relay coils or switches as well as connections to or within the protective relays .
- the DC power system includes plus and minus polarity DC busses, as well as extensive equipment connections.
- DC grounds on the plus and minus busses can be detected by conventional DC monitoring systems which are typically located in the vicinity of the battery portion of the system.
- DC grounds in the remainder of the DC supply system are usually very difficult and time-consuming to locate.
- an indication by the conventional monitoring system of a DC ground will result in an alert to a repair crew, which has the task, upon arrival, if the DC ground is not found to be on the plus or minus bus, of sequentially removing from the substation power circuit each protective relay or other piece of equipment so as to locate the DC ground.
- the present invention is a DC monitoring system which is for use in electric power substations having at least one DC supply system which includes positive and negative DC supply busses, the substation including at least one protective relay which is powered by said DC supply, the monitoring system comprising: a first portion which is responsive to voltage between one supply bus and ground and voltage between said two supply busses to determine the presence of a DC ground in the DC supply system and whether the DC ground is closer to one supply bus line than the other and which provides an indication thereof; and a second portion which includes means for measuring voltage at selected contact input connections of the protective relay; means for comparing said contact input voltages against a selected range of standard voltage values; and means providing an indication when the measured voltage is within said range, wherein the combination of the indications from the first portion and the second portion is useful in locating the origin of the DC ground in the DC supply system.
- Figure 1 is a simplified diagram illustrating a portion of a substation protection system, including the DC supply therefor.
- FIG. 2 is a block diagram of one portion of the DC monitoring system of the present invention.
- Figure 3 is a diagram showing another portion of the DC monitoring system of the present invention.
- Figure 4 is a table showing how the information provided by the system of the present invention can be used to locate an inadvertent DC ground within a power substation.
- an electric power substation which serves a particular geographical region with electric power will include a protective system involving a variety of equipment, all of which require power for operation and communication.
- This power is typically provided by a centralized DC station battery system which includes in general a battery charger for maintaining the output of the battery within a specified range.
- the battery output voltage may differ from installation to installation.
- DC power could in some cases be provided by a distributed DC system, in which separate batteries are used for each piece of equipment, i.e. the protective relays, or small groups of equipment .
- a typical centralized system uses a 125 volt DC battery, and the following description assumes that voltage level.
- a typical voltage range for a 125 VDC nominal system is from 108 VDC (low voltage) to 150 VDC (maximum voltage) .
- the latter voltage level is often referred to as an equalize voltage and is commonly used with lead-acid batteries.
- Some systems may have two DC supplies, with different voltage outputs. It should be understood that the present invention is also applicable to substation DC power systems that operate at outputs of other than 125 volts.
- a 125 volt DC system will comprise two groups of series -connected batteries, each group producing 62.5 volts. Each group of batteries includes 25-30 series-connected batteries, typically lead-acid batteries. A single battery charger will charge both groups of batteries simultaneously.
- a power line protection system present in a substation will include a large number of protective relays, various instrument transformers and circuit breakers with related trip coils and contacts.
- Figure 1 shows a two-battery set producing 125 VDC and 48 VDC, which would ordinarily include an independent battery charger (not shown) for each battery.
- the circuit shown in Figure 1 shows typical DC supply connections for a three-pole trip and reclose breaker application using communication-assisted tripping.
- the 125 volt battery 10 is used for breaker tripping, closing and control, while the 48-volt battery 11 is used for the communication equipment, assisted trip and control.
- the present explanation will focus on the 125-volt system.
- the 125 volt battery 10 includes four plus and minus
- Battery 10 with its associated system wiring and connections is responsible for energizing trip coils 20 and 22 when trip contacts 24 and 26 close in response to a command from the protective relay.
- Trip coil 22, trip contact 26 and the associated wiring form a redundant trip circuit for increased security.
- the power system circuit breaker controlled by the protective relay is closed and breaker contacts 28 and 30 are closed. Closure of trip contacts 24 and 26 by the protective relay thus results in a current path through the associated trip coils, which in turn results in the circuit breaker associated with the trip coils opening.
- Close coil 32 (bus lines 18a-18b) is energized by the DC supply system when the reclosing circuit of the protective relay signals its associated breaker to close by closing breaker contact 34. Closure of the close contacts 34 by the protective relay will result in current flowing through close coil 32, resulting in the closing of the system circuit breaker following operation of the breaker contacts 35.
- the DC supply system also provides a communication link between contact 37 and the protective relay contact input 38 as well as communicating the closure of control switch 40 to contact input 42.
- Control switch 40 is typically an external, manually operated switch, controlled by an operator off of the front panel of the protective relay control terminal.
- the DC supply provides power for the power supply of the protective relay, as well as power to communication equipment if said equipment is external to the protective relay.
- the 48-volt battery provides power for communicating a permissive trip signal from a remote line terminal to the protective relay, by virtue of the closure of the control contacts 44, which energizes input contact 46 of the protective relay.
- the system of Figure 1 includes conventional DC monitoring systems for each battery 10 and 11.
- the monitoring system includes a series connection of resistors 50 and 52, with a center connection to substation ground. Resistors 50 and 52 form a typical DC-ground detector found in most current substations. Typically, each resistor is 10K ohms. In some cases, two small lamps or voltmeters are used in place of the resistors.
- the voltage across or the current through each of the resistors 50, 52 is measured to determine the presence of inadvertent DC grounds. When there is no DC ground, the voltage across the resistors will be the same and there will be no current to ground. In the event of an inadvertent ground, voltage across one resistor will be higher than the other (in the case of two lamps, one will be brighter) .
- the resistor having the lowest voltage indicates the particular side of the DC bus (plus or minus) which is associated with the inadvertent ground. As indicated above, however, this system is only able to determine if the DC ground is actually on either bus directly or which bus is closer to the inadvertent ground if the ground is not on a bus.
- the monitoring system cannot provide any additional information; if the ground is in the equipment, which it most frequently is, the technician/operator must carefully remove each piece of equipment from the system in turn to determine the location of the DC ground, which occurs when the DC ground indicator disappears when the grounded circuit is de-energized.
- the system of the present invention for providing a more particular determination of DC ground location is located in Figure 1 at 60 (power supply at 61) and shown in more detail in Figure 2. It is important to note that the present system requires no additional connections or leads from the DC battery source or the protective relay or other equipment . The connections to the present system are made directly across the DC power lines to the relay (DC plus and minus bus lines) .
- the circuit 60 provides two voltage values CMDC and DMDC at the outputs of voltage amplifiers 62 and 64.
- the input to amplifiers 62 and 64 is through a resistor network comprising resistors 66-69. These resistors, because of their relatively large values (resistors 66 and 69 are 22 M ⁇ ) compared to the values of resistors 50 and 52, draw very little current from the battery (less than 3 microamps) .
- the DC ground detector of the present invention thus does not adversely affect the operation of conventional DC ground detectors comprising resistors 50 and 52.
- Amplifier 62 is connected between the positive DC bus 12a and ground of Figure 1. Hence, it provides what is referred to as a common mode voltage, which is proportional to approximately half of the battery voltage, i.e. 62.5 volts.
- Amplifier 64 is connected between the positive and negative DC busses 12a and 12b and therefore provides what is referred to as a differential mode voltage, which is proportional to the full battery voltage, i.e. 125 volts.
- the difference between the common mode voltage and the differential mode voltage value is a voltage value which is proportional to the voltage between the negative DC bus 12b and ground.
- the circuit of Figure 2 provides protection against "nuisance” alarms which may be caused by transient conditions or other factors. A “dead band” of voltage is created to provide this protection.
- the output of the differential mode amplifier 64 is applied to multipliers 70 and 74.
- the multiplier value is M/2, while in multiplier 74, the multiplier value is 1/2M, where M is a selected constant having a range of 1 ⁇ M ⁇ 2.
- the value of M in the present embodiment is 1.03. This value provides a reasonable level of security against false inadvertent DC grounds .
- multiplier 70 is then applied to the negative input of a comparator 76, while the output of multiplier 74 is applied to the positive input of a comparator 78.
- the common mode output of amplifier 62 is applied to the positive input of comparator 76 and the negative input of comparator 78. Under normal operating conditions, the outputs of both comparators will be low, indicating no DC grounds. If the common mode value (positive bus to ground) is greater than the differential mode value multiplied by M/2, then the output of comparator 76 goes high. Conversely, if the differential mode value multiplied by 1/2M is greater than the common mode value, then the output of comparator 78 goes high.
- comparators 76 and 78 are applied to an OR gate 80, a high output of which initiates a time-delay pickup and dropout timer 82.
- Timer 82 is set to prevent erroneous detection of inadvertent DC grounds due to transient conditions and provides time discrimination for inadvertent grounds detected by voltage monitors around open relay contacts. In the embodiment shown, the time-delayed dropout portion of the timer is set equal to zero so that the output of the timer terminates when the input thereto terminates.
- the output of timer 82 is applied to AND gates 84 and 86.
- the other inputs to AND gates 84 and 86 are the outputs of comparators 76 and 78, respectively.
- a high output of AND gate 84 is referred to as an NDCG signal, indicative of an inadvertent ground on the negative side (bus) of the supply, while the output of AND gate 86, referred to as a PDCG signal, is indicative of an inadvertent DC ground on the positive side (bus) of the supply.
- Figure 3 shows the effect of the circuit of Figure 2 relative to the declaration of DC grounds.
- the relay With a differential mode value of 130 volts, the relay will provide an alarm when the common mode voltage is greater than 63.1 volts or less than 66.95 volts.
- the output of the common mode amplifier will be 71.3 volts, which leaves a small margin of slightly greater than 1 volt between an actual DC ground condition (when the battery is at 140 volts) and a normal condition when the battery is low (but not low enough to produce an alarm) . This close margin could easily result in errors in DC ground recognition.
- the output of the common mode amplifier 62 will be 139.8 volts DC and the output of the differential mode amplifier 64 will be 140 volts DC.
- the present invention in addition to the common mode and differential mode voltage measurements, including the circuit of Figure 2 which provides a determination of NDCG (negative DC ground) and PDCG (positive DC ground) and the associated alarms, the present invention includes relay contact input voltage measurements which make possible a more accurate and precise determination of the location of inadvertent DC grounds within the substation, including the substation protective equipment.
- an electric power substation will have a plurality of equipment, including protective relays. If each of the protective relays has a DC monitoring circuit as shown in Figure 2, an alarm from any of the DC monitors will indicate that there is an inadvertent DC ground in the DC system on the plus or minus DC bus or, if not on the busses, that the DC ground is closer to one bus than the other.
- the contact input measurements from each of the relays will provide additional information as to which of the relays has the DC ground and the location of the DC ground associated with that relay.
- location of inadvertent DC grounds becomes more systematic and accurate.
- the voltage at each of the contact inputs of a relay is compared against fixed thresholds.
- the contact inputs include contact input 40, among others.
- the contact input will have a nominal value of voltage for operation. The nominal or normal value is herein defined as the measured differential mode voltage value.
- a contact input will assert, i.e. close, when the voltage at the contact input is over 50 percent of the nominal voltage. However, between 75 percent and the full nominal value, the contact input will assert and there will in addition be no DC ground alarm. If the applied voltage is greater than 1.3 times the nominal voltage, then the contact input is either defective, incorrectly configured or the battery charger is malfunctioning. An alarm is provided and the contact input is asserted.
- Table 4 shows a representative sampling of various possible DC ground locations relative to a protective relay and the resulting PDCG and NDCG outputs and the alarm condition of several relay contact inputs.
- location No. 1 is a ground on the VDC1 bus, with all the relay contacts on the relay open. In that case, there is a PDCG alarm, but no alarms from any of the contact inputs. This means that the DC ground is not between any of the open relay contacts and the contact inputs shown. If all of the 125 volt DC contacts are open (which can be readily ascertained) , the inadvertent ground must be on one of the DC busses, i.e. busses 12, 14, 16 or 18.
- the DC monitor detects an inadvertent DC ground, and one of the contact inputs also indicates a ground, the actual location of the ground can be pinpointed with greater accuracy. For example, where there is a ground between switch contact 42 and contact input 40, PDCG signal will assert with switch contact 42 open, while when the control switch 42 is opened, the relay logic will assert NDCG, as will input contact 40.
- the contact input voltage can also be compared against adaptive thresholds as opposed to fixed thresholds.
- the voltage measured at the contact inputs is compared against a preselected fraction of the actual differential mode voltage between the two DC supply busses (positive and negative) .
- the total range of voltages on the contact input might cover 30 to 150 volts for a 125 -volt nominal voltage value.
- a voltage on the contact input of less than 30 volts would be considered as a de-energized input, while a voltage of greater than 30 volts but less than a selected fraction or percentage of the total differential mode voltage (as measured) would result in a DC ground detection alarm.
- this selected fraction is 55/100 or 0.55.
- a range of values is 0.50-0.75, depending upon the degree of security desired.
- the measured voltage at the contact input would be another selected fractional value of the differential mode voltage, but less than the maximum of 150 volts. Above 150 volts would be an indication of charger malfunction.
- the second fraction value is 56/100 or 0.56. The second fraction will always be slightly greater than the first fraction. For a 140-volt measured differential mode voltage value, the range of voltage which would result in a DC alarm is 30-77 volts.
- the adaptive threshold provides a more reliable indication of a DC ground, given the relatively wide range of nominal voltages which may be available to the contact input.
- a system for detecting DC grounds in a DC supply system for a power system substation which results in an increased ability to readily identify the location of DC grounds within the substation with significantly greater particularity than heretofore possible.
- the disclosure above concerns a single or dual battery system for an entire substation, serving a plurality of individual equipment, including numerous protective relays
- the present system of DC ground monitoring could work with a "distributed" DC supply arrangement, in which there are a plurality of DC supply systems within a substation, each DC supply serving a few or even one piece of equipment, such as a single protective relay.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
BR9914383-6A BR9914383A (en) | 1998-10-08 | 1999-10-06 | Direct current monitoring system for use in electrical substations |
EP99951832A EP1119891A4 (en) | 1998-10-08 | 1999-10-06 | A protective relay-based monitoring system of dc power within an electric power substation |
AU64189/99A AU761774B2 (en) | 1998-10-08 | 1999-10-06 | A protective relay-based monitoring system of DC power within an electric power substation |
CA002346732A CA2346732C (en) | 1998-10-08 | 1999-10-06 | A protective relay-based monitoring system of dc power within an electric power substation |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/169,370 | 1998-10-08 | ||
US09/169,370 US6084755A (en) | 1998-10-08 | 1998-10-08 | Protective relay-based monitoring system of DC power within an electric power substation |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2000021175A1 true WO2000021175A1 (en) | 2000-04-13 |
Family
ID=22615387
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1999/023333 WO2000021175A1 (en) | 1998-10-08 | 1999-10-06 | A protective relay-based monitoring system of dc power within an electric power substation |
Country Status (6)
Country | Link |
---|---|
US (1) | US6084755A (en) |
EP (1) | EP1119891A4 (en) |
AU (1) | AU761774B2 (en) |
BR (1) | BR9914383A (en) |
CA (1) | CA2346732C (en) |
WO (1) | WO2000021175A1 (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2007035725A2 (en) * | 2005-09-19 | 2007-03-29 | Schweitzer Engineering Laboratories, Inc. | Method and apparatus for routing data streams among intelligent electronic devices |
US7755872B2 (en) * | 2006-09-14 | 2010-07-13 | Schweitzer Engineering Laboratories, Inc. | System, method and device to preserve protection communication active during a bypass operation |
US8040139B2 (en) * | 2009-02-16 | 2011-10-18 | Maxim Integrated Products, Inc. | Fault detection method for detecting leakage paths between power sources and chassis |
US8598897B2 (en) * | 2010-01-26 | 2013-12-03 | Maxim Integrated Products, Inc. | Isolation monitoring system and method utilizing a variable emulated inductance |
CN106707083A (en) * | 2016-12-28 | 2017-05-24 | 国家电网公司 | Substation direct current grounding detecting device |
JP6932964B2 (en) * | 2017-03-25 | 2021-09-08 | 東京電力ホールディングス株式会社 | DC power supply circuit disconnection discriminator and wiring discriminator |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3619775A (en) * | 1969-11-25 | 1971-11-09 | Pulse Monitors Inc | Polarity and voltage level detecting test probe |
US3801898A (en) * | 1971-06-16 | 1974-04-02 | Gen Electric Canada | Dc bus resistive path to ground fault detector |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4929901A (en) * | 1985-09-06 | 1990-05-29 | Dorr Kimball | DC ground fault detection |
US5530363A (en) * | 1994-10-31 | 1996-06-25 | John Gaughan | DC ground fault detecting apparatus with an auto-null circuit and method |
-
1998
- 1998-10-08 US US09/169,370 patent/US6084755A/en not_active Expired - Lifetime
-
1999
- 1999-10-06 WO PCT/US1999/023333 patent/WO2000021175A1/en not_active Application Discontinuation
- 1999-10-06 AU AU64189/99A patent/AU761774B2/en not_active Ceased
- 1999-10-06 CA CA002346732A patent/CA2346732C/en not_active Expired - Fee Related
- 1999-10-06 EP EP99951832A patent/EP1119891A4/en not_active Withdrawn
- 1999-10-06 BR BR9914383-6A patent/BR9914383A/en not_active IP Right Cessation
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3619775A (en) * | 1969-11-25 | 1971-11-09 | Pulse Monitors Inc | Polarity and voltage level detecting test probe |
US3801898A (en) * | 1971-06-16 | 1974-04-02 | Gen Electric Canada | Dc bus resistive path to ground fault detector |
Also Published As
Publication number | Publication date |
---|---|
BR9914383A (en) | 2002-01-15 |
EP1119891A1 (en) | 2001-08-01 |
AU761774B2 (en) | 2003-06-12 |
EP1119891A4 (en) | 2002-03-20 |
AU6418999A (en) | 2000-04-26 |
CA2346732C (en) | 2008-08-05 |
US6084755A (en) | 2000-07-04 |
CA2346732A1 (en) | 2000-04-13 |
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