WO2012042318A1

WO2012042318A1 - Powerless reset in a self powered relay

Info

Publication number: WO2012042318A1
Application number: PCT/IB2011/001303
Authority: WO
Inventors: B. Patel Hardik; Parmar Jatin; Y. Shafi Mohammed; Suthar Niraj
Original assignee: Abb Technology Ltd
Priority date: 2010-10-01
Filing date: 2011-06-10
Publication date: 2012-04-05

Abstract

A self powered relay having a feature for powerless trip reset in the relay is provided. The relay makes use of one or more capacitors (120, 130) for storing energy for trip operations during the normal condition in an electrical system. The stored energy is utilized during a trip reset operation when there is no power supply derivable from the current flowing in the electrical path of the equipment being protected. The charging of the storage capacitors is enabled with help of a switch in the charging/discharging path of the capacitors and a microcontroller that controls the switch to operate the switch algorithmically for charging operation. The relay uses an electromagnetic flag (110) for capturing the trip state of the relay. The trigger for trip set in the electromagnetic relay is generated by the relay and the reset of the electromagnetic flag is generated by a user of the relay with help of a push button (230) or devices alike. A method for enabling reset of a trip state in the self powered relay is also provided.

Description

POWERLESS RESET IN A SELF POWERED RELAY

Field of the Invention:

The present disclosure relates generally to circuit interruption arrangements, such as current measurement and sensing arrangements used by overload/over-current relays which are powered from the circuit path they are arranged to interrupt (self-powered).

Background of the Invention:

The use of relays is widespread in modern-day residential, commercial and industrial electric systems and they constitute an indispensable component of such systems for providing protection against over-current conditions and earth-fault protection. On an event of fault, example an over-current condition in the power system, the protection relay provides a trip signal to the interrupting device such as circuit breaker to trip the power to the power equipment being protected. In such event, the protection relay is required to have a "trip" indication in the protection relay even after the trip so that the operator/user associated with the power system is aware of the trip condition.

In auxiliary powered relay, power supply for the protection relay provided through external source, the trip event is notified with a "trip" LED indication. However, in a self powered relay, power supply derived from the current in the circuit path arranged for interruption, the provision of "trip" LED indication requires additional circuitry. This is so because after the current interruption, an event in order to protect the power equipment in fault condition, the power supply to the protection relay is affected.

One circuit implementation (prior-art) for a self powered relay is with use of Bi-stable Flag/Flip indicator, which ensures availability of trip indication even in absence of the primary CT current. This flag can be electromagnetic or electro mechanical type. The electro mechanical type of flag is more common but it demands bigger size and more power compared to the electromagnetic flag. The advantage of the electro mechanical type of flag is that it does not require voltage supply for "reset" operation. Therefore, the trip can be acknowledged anytime, even in absence of the current transformer (sensor for measurement of current from which the power for the protection relay is derived) primary current.

Further, it is common to have the electro mechanical flag provided external to the relay because of the size constraints and the user/operator has to make connections from relay to the external flag. In an event of wrong/no connection, there will not be a trip indication.

On the other hand, the electromagnetic flag demands very less space and power compared to the electromechanical flag and can be easily accommodated within a relay to provide reliable indication. But this kind of flag requires voltage supply to operate (Set/Reset).

Set action is being done by relay in the event of trip and reset action is expected to be carried out by the operator to acknowledge the trip. The reset action may be enabled through external battery/voltage supply but then this solution has limitations of requiring external connection and being dependent on an external source/device. The reset action may be enabled when the power is restored through power from the current transformer (CT) primary current. However, there is risk of not being able to distinguish (identify/discriminate) the trip when the next trip event occurs before resetting of the previous "Set" flag.

Therefore it is desirable to reset the flag with a power that is easily available within the relay, even in absence of the primary CT current to draw power for this purpose. It is an object of the invention to provide an effective means for the self-supplied protection relays to indicate the trip status for the operator.

Summary:

According to one aspect of the present invention, a self powered relay having a feature for powerless trip reset in the relay is provided. The relay makes use of one or more capacitors for storing energy for trip operations. The stored energy is specifically utilized during a trip reset operation when there is no power supply derivable from the current flowing in the electrical path of the equipment being protected.

In an embodiment of the invention, the mechanism for controlled charging of the one or more capacitors to store energy for the trip operation in the relay is provided. The mechanism is enabled with help of a switch in the charging/discharging path of the one or more capacitor and a microcontroller that controls the switch to operate the switch at an algorithmically determined instant of time and duration during the normal operation of the relay. The controlled charging specifically ensures that the current measurement is not affected due to charging of the storage capacitors. The mechanism also has a biasing circuit to control the amount of current flow for charging of the capacitor.

In another embodiment of the invention, an electromagnetic flag is used for capturing (includes indicating) the trip state of the relay. A trigger mechanism for set and reset of the electromagnetic flag involves providing a voltage pulse at the set or reset winding of the electromagnetic flag. The relay generates a trigger to set the trip in the electromagnetic flag with help of the microcontroller that compares the condition for the trip with the computation/measurements made by the relay. The trigger for reset of the electromagnetic flag is generated by a user of the relay with help of a push button or devices alike.

In another aspect of the present invention, a method for enabling reset of a trip state in a self powered relay is provided. The method comprises the steps of: a. Charging one or more capacitors in a controlled manner for storing energy for a trip reset operation; and

b. Having an electromagnetic flag be operated using the stored energy in the one or more capacitors released on receiving a trigger from a user of the self powered relay.

The method is characterized by having the trip reset operation in the self powered relay carried out using the electromagnetic flag when there is no power supply derivable from the at least one phase current that the self powered relay is measuring i.e. when the trip is activated resulting in circuit interruption.

Brief Description of the Drawings:

Other features and advantages will become apparent to those skilled in the art upon reading the description of the preferred exemplary embodiments in conjunction with the accompanying drawings, wherein: Figure 1 shows an exemplary scheme for activation of a trip flag with according to the present invention;

Figure 2 illustrates the operation of the scheme shown in Figure 1 ;

Figure 3 shows a block diagram of modules of a self supplied relay associated with Figure 2; and

Figure 4 provides a method for operation of the scheme shown in Figure 1

Detailed Description:

The invention provides an efficient means for the self-supplied protection relay to have trip indication and enable reset function even in absence of the primary current in the CT through which the relay is drawing power for its function. For this purpose, the self-supplied relay is designed to enable some stored energy internal to the relay for enabling reset of the flag in the absence of CT currents, after the circuit breaker (CB) has tripped.

Figure 1 illustrates a scheme 100 for providing power for reset function in a self- powered three phase over current and earth-fault protection relay. The relay has an internal electromagnetic flag depicted by numeral 1 10 and capacitors depicted by numeral 120 and 130 for storage of energy. The stored capacitor energy is used to "Reset" the electromagnetic flag. The design allows resetting of flag up to minimum period of 3days after tripping CB, in the absence of CT currents. It can set the flag & store the required energy (for resetting the flag) along with issuing a trip command even when small current flows in a single phase.

Separate storage capacitors are used for set function depicted by numeral 120 and for reset function depicted by numeral 130. The capacitors are charged in a controlled manner so that there is no impact on normal functionality (i.e. measurement accuracy, power on trip time) of the relay.

The electromagnetic flag operates as a result of magnetic field generated by electric current. These devices do not require driving mechanisms such as springs as the magnetic field itself provides the required driving force. The electromagnetic flags have two main elements, an electromagnet core and a permanently magnetized disk that are used as an indicator. The flag requires a voltage pulse at Set (140) and Reset (150) windings for its function. On application of the voltage pulse at one of the winding, a magnetic flux is created in clockwise/anticlockwise direction in the magnetic core depending on the winding on which the voltage pulse was applied. As a result, the disk which is permanently magnetized will align itself in such a way that the flux passing through the core will have the lowest reluctance path.

As an example of the specification of the electromagnetic flag used in the construction of the relay, the following details are provided:

Overall Size: 1 1.43mm(0.45in)x 1 1.43mm(0.45in)

Weight: 4.0g (0.14oz ) max

Coil Drive: Current pulse of 1.5 millisecond duration

270mA minimum amplitude

4.0V minimum voltage

Coil Resistance a 20C: 12ohms±20%

Power to Maintain Displayed Data: Zero

Operating Temperature: -40C to 85C

Figure 2 illustrates the charging and the discharging path for the storage capacitors prepared for reset operation:

The charging path 210 is Vcc Flag - D3 -^Capacitors ->S4 -^Ground

The self-power relay has a microcontroller (not shown in the figure) to control the electronic switch S4. The microcontroller enables S4 only when the relay has sufficient energy i.e. when there is no (or not sufficient) current through CTs, the switch disconnects the storage capacitors from ground. The power sensing and control of the switch is achieved through use of simple electronic circuits and by having the microcontroller provide the necessary synchronization and trigger for circuit operations. Also, the electronic circuit includes biasing in such a way that it limits the maximum charging current through the switch S4. In this embodiment, the biasing is provided with use of a resistance 240. Thus, the charging of storage capacitors does not have any noticeable impact on the normal operation (particularly, on phase current measurement) of the relay. Thus with help of the microcontroller and the biasing circuits, the instant for charging, the duration of the charging and the amount of current for charging are controlled electronically and algorithmically.

The discharging path 220 for storage capacitors is Capacitors ->D4 -PRESET winding of Flag ->S2 -> Capacitors

When user push the push button for RESET, 230, S3 will be on, which makes S2 "ON" for small duration (3-5 m Sec). So for that small duration, voltage across the storage capacitors will be applied to RESET winding of Flag and thus Flag will reset.

For the SET operation, the charging path for the storage capacitors for SET operation CI is Vcc_Flag -»Dl ->Rl ->C1 ^Ground

Value of CI is not very high. So there is no need of controlled charging for it, as it is needed for the storage capacitors for RESET operation. However, depending on the energy ratings one may design controlled charging of the capacitors as described for the Reset function.

The controller in the relay issues "Trip" command and "Flag SET" command when it detects a valid Fault (in any of the phases or Earth) or when it detects a Remote Trip input. The "Flag SET" command makes S 1 ON for about five millisecond and for that small duration, the voltage across CI will be applied to SET winding of the electromagnetic Flag 1 10 to have the Flag set.

The circuitry preferably has electrolytic capacitors for energy storage requirement. In an embodiment of the invention, miniature aluminum electrolytic type capacitor is used for energy storage. In normal operation, maximum of 10 volt is being applied across the capacitors. This capacitor is being used for storage purpose and not for continues charging/discharging as the SET and RESET functions of a relay are not frequent. So its life will be much more than the claimed endurance period.

When user pushes the RESET button 230, the energy stored in the capacitors will discharge (up to 5 m Sec only) through the RESET winding. Maximum discharging current is limited by the RESET winding impedance (120hm). So the maximum discharge current is 10V/12Ohm = 0.833Amp. Also the energy is stored at l OVolt. So the storage as well as SET/RESET operations are safe.

In an embodiment of this invention, the protection relay with the energy storage scheme 100 is provided. The block diagram of the protection relay is provided in Figure 3. The self-supplied relay has two-stage (low-set and high-set) non-directional over-current and earth-fault protection stages. The relay is designed to support Definite time and IDMT (inverse definite minimum time) characteristics for both phase and earth-fault protection. The operation of the low-set over-current stage I> and the low-set earth-fault stage I0> is based on definite time or inverse time characteristic, as selected by the user. The high-set stage has instantaneous and definite time characteristics.

When the phase current exceeds the set operate value at definite time operation or the calculated operate time at inverse time operation elapses, the over-current unit operates. In the same way the high-set stage I» of the over-current unit operates when the set operate time elapses.

When the earth-fault current exceeds the set operate value at definite time operation or the calculated operate time at inverse time operation elapses, the earth-fault unit operates. In the same way the high-set stage 10» of the earth-fault unit operates when the set operate time elapses.

The relay also includes one external binary input 310, which is controlled by an external control voltage (24-240 V AC/DC). This input can be utilized to give an output trip command. Whenever controller detects valid Fault (in any of the phases or Earth) or detects Remote Trip input, it issues "Trip" command 320 and "Flag SET" command 330. The RESET for the relay is implemented using the scheme 100 with help of the push button 230 for flag reset using the stored energy 130 for the flag reset. The relay is also provided with a failsafe trip 340 for the relay to fail safely by issuing trip output 320, particularly when the microcontroller has failed and the phase current level is found greater than the limiting levels (example 20 times the CT rated current) and for a specific limiting duration (example 40 msec).

Thus, the relay has a controller to detect a valid fault (in any of the phases or Earth) and to detect a Remote Trip input by issue of "Trip" command and "Flag SET" command and also has a protection for fail safe operation. The RESET for the "Trip" state is provided using the scheme 100 described in the invention for enabling reset of a trip state in the self powered relay. The method for reset is illustrated in Figure 4 that depicts the two main steps; a) Charging of capacitors in a controlled manner for storing energy for a trip reset operation depicted by numeral 410; and b) having an electromagnetic flag operated using the stored energy in the one or more capacitors released on receiving a trigger from a user of the self powered relay depicted by numeral 420. The method 400, thus provides utilization of the stored energy for reset operation when the relay is unable to derive power from the current sensors (current transformer) used for measurement of phase currents.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

We Claim:

1. A self powered relay, for providing electrical protection in an electrical systems by issue of a trip output on detection of a fault, characterized in that the self powered relay comprises:

a. One or more capacitors for storing energy for a trip operation; b. A mechanism for controlled charging of the one or more capacitors to store energy for the trip operation;

c. A trigger mechanism to trigger a trip operation by utilizing the stored energy in the one or more capacitors; and

d. An electromagnetic flag for capturing the state of the trip operation on receiving the trigger from the trigger mechanism.

2. The self powered relay as in claim 1 , wherein the trip operation comprises of a Set and a Reset operation in the self powered relay.

3. The self powered relay as in claim 1 , wherein the one or more capacitors stores energy for the trip operation during the normal state of the electrical system.

4. The self powered relay as in claim 1, wherein the mechanism to control the charging of one or more capacitors to store energy for the trip operation is provided by having a microcontroller controlling the instant and duration of charging of the one or more capacitors.

5. The self powered relay as in claim 1, wherein the mechanism to control the charging of one or more capacitors to store energy for the trip operation is provided by having a biasing circuit for controlling the amount of current provided for charging.

6. The self powered relay as in claim 1 and claim 2, wherein the trigger mechanism to trigger a trip operation for Set operation is enabled by use of a microcontroller that identifies a fault in the electrical system.

7. The self powered relay as in claim 1 and claim 2, wherein the trigger mechanism to trigger trip operation for a reset operation is provided with use of a push button switch operated by a user of the self powered relay.

8. The self powered relay as in claim 1 , wherein the electromagnetic flag for capturing the state of the trip operation is operated for the trip Set and Reset operation.

9. A method for enabling reset of a trip state in a self powered relay, the self powered relay designed to derive its power supply from at least one phase current that the self powered relay is measuring to offer electrical protection in an electrical system, the method comprising the steps of:

a. Charging one or more capacitors in a controlled manner for storing energy for a trip reset operation; and

b. Having an electromagnetic flag be operated using the stored energy in the one or more capacitors released on receiving a trigger from a user of the self powered relay;

Wherein the method is characterized by having the trip reset operation in the self powered relay carried out using the electromagnetic flag when there is no power supply derivable from the at least one phase current that the self powered relay is measuring.

10. The method as in claim 9, wherein the charging of one or more capacitors in a controlled manner is managed by controlling the instant of charging and/or duration of charging and/or the amount of charging of the one or more capacitors.