WO2014087326A1

WO2014087326A1 - A protection and control apparatus with a programmable display

Info

Publication number: WO2014087326A1
Application number: PCT/IB2013/060589
Authority: WO
Inventors: Nayan SHAH
Original assignee: Abb Technology Ltd
Priority date: 2012-12-04
Filing date: 2013-12-03
Publication date: 2014-06-12

Abstract

An intelligent electronics device, lED, (700) for effective configuration and monitoring of protection and control functions in an electrical subsystem in a power system is provided. The lED has an human machine interface (770) unit that displays an operating point value derived from measured signal parameters and displays an operating region for protection or coordination function derived from operating limit information available with the lED. The display captures movement of the operating point value as a trace. Displaying of the operating region comprises of displaying a first operating region from the one or more operating limit information available with the lED and displaying atleast one second operating region of the lED from an update of the one or more operating limit information in the human machine interface unit of the lED.

Description

A PROTECTION AND CONTROL APPARATUS WITH A PROGRAMMABLE

DISPLAY

FIELD OF THE INVENTION

The invention relates to the field of electrical power equipment. The invention specifically relates to effective configuration and monitoring of protection and control functions used for protection of electrical power equipment.

BACKGROUND OF THE INVENTION

A conventional Intelligent Electronic Device (IED) for protection, control and automation in a power system network has a graphical display that is available with the IED either as a local display provided with the IED or as a remote display provided in a client station for monitoring or configuring the control and protection function in a power system. The display provides with text and graphical information about operating values, parameter setting, event records, active binary input/output information, active alarms, active indicators, measurement value, single line diagram with status of various power system apparatus etc. For a power systems engineer apart from the information available conventionally on a local or remote display that act as an Human Machine Interface (HMI) for the engineer, it is desirable to have additional online information that may depict design and operating limits of a feature of interest (eg protection function) from a power system control device. Display of such information is useful to analyze dynamic behavior of operating point for a protection function over a period of time to judge proper configuration and utilization of the protection device. For example, one may want to know, the extent to which a power equipment or power system is used/stressed in a normal operating condition and also review the settings of over and under operating limits etc. Thus, display of dynamic behavior of the operating point can help to better visualize and understand the various states in a power system. One can also visualize if the settings are configured appropriately or not, especially for complex functions like distance / admittance / differential / directional protection etc.

Thus there is a need for a display that provides design and operation information to help configure and design the protection and control functions in a powers system. BRIEF DESCRIPTION OF THE INVENTION

In one aspect of the invention, a method for displaying operating limit characteristics of an electrical subsystem in a power system on a graphical user interface of an Intelligent Electronic Device (IED) is provided. The method comprises the steps of a) having an operating limit value configured for a protection function in the IED; b) calculating an operating region from the configured operating limit value in the IED in one part and in another part a) measuring at least one signal parameter from the electrical subsystem in the power system; calculating an operating point value for the protection function from the at least one measured signal parameter; and c) displaying the operating region along with the operating point value on the graphical user interface of the IED.

In one embodiment of the invention, the IED displays the operating point value as a trace displaying movement of the operating point value on the graphical user interface.

In another embodiment of the invention, the IED displays multiple operating region corresponding to multiple protection functions in the IED and also changes in the operating region due to change in a particular protection setting. Such features are programmable in the IED. Such display abilities are illustrated with examples that demonstrates use of displaying a first operating region corresponding to a first configured operating limit value along with displaying of a second operating region corresponding to a second configured operating limit value during configuration of the IED. The information for configuration any of the operating region or for displaying corresponding operating point value can be obtained from a remote device in the electrical subsystem.

In another aspect of the invention, an intelligent electronics device (IED) for protection and control function in an electrical subsystem in a power system is provided. The IED has a base unit for measuring and processing at least one signal parameter in the electrical subsystem and generate a trip signal derived from comparison with an operating limit value provided in the IED; and a human machine interface (HMI) unit for displaying an operating point value derived from the at least one signal parameters and for displaying an operating region derived from the operating limit value provided in the IED.

In another embodiment, the IED provides protection based on measurement of electrical (for example current, voltage etc) and physical signal (for example temperature, pressure etc).

In yet another embodiment, the IED is capable to provide an operating point value or an operating limit value to a remote device in the electrical subsystem and wherein the remote device is a client station or another IED with a HMI unit. The remote device may be any device in a substation automation system or supervisory control and data acquisition (SCAD A) system.

In yet another embodiment, the IED with programmable display (HMI unit) is provided for use in configuration of an operating limit value in the IED for protection function that also includes coordinating protection in an electrical subsystem.

In yet another embodiment, the IED with programmable display is provided for use of displaying the configuration information depicted as operating region along with displaying an operating point value (operating point) that illustrates the operating status in the electrical subsystem. The programmable display is also capable of recording dynamic behavior of an operating point value in the IED. The recorded information also includes the temporal changes in operating limit values and corresponding changes in operating region in any manner suitable through programming configuration for display and recording in the IED.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages will become apparent to the person skilled in the art upon reading the description of the preferred exemplary embodiments in conjunction with the accompanying drawings, wherein:

Figure 1 is an illustration of under impedance protection;

Figure 2 is a display for displaying operating limit characteristics;

Figure 3 is a display for change in operating limit characteristics based on protection settings; Figure 4 is showing the dynamic operating characteristics for under impedance protection;

Figure 5 is a display illustrating different stages of an overcurrent protection in a device to support user in configuration;

Figure 6 is an illustration for configuring overcurrent protection in a protection device; and

Figure 7 is a block diagram depicting the protection and control apparatus with a programmable display.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention provides for an intelligent electronic device (IED) with a display that provides information about operating limit characteristics to help visualize protection and control functions in a powers system. The information can be provided and received (locally or remotely) and can also be consolidated with information from other IEDs present in a power system network to visualize, effective configure including coordination amongst devices. The displayed information will help to visualize the complex function and to configure the settings with ease.

For example, in case of configuring protection setting for a protection function, the protection function in an IED is configured by defining an operating limit and calculating an operating region corresponding to the configured operating limit. When any of the power system parameters measured through the IED and associated with the protection function falls within the operating limits or operating region, the IED would issue a trip signal. In normal conditions, the power system parameters associated with the protection function would remain outside the operating limit of the protection function and in abnormal conditions if any of the power system parameters measured and associated with the protection function enters (fall within) the operating limit of the protection function results into a trip. The boundary of the operating limit is defined by setting the associated protection parameter appropriately. Many times for complex functions it is difficult for users to configure the settings appropriately. The behavior of operating limits may also be useful to understand interdependencies or complexities involved in configuration.

A programmable display for a protection and control apparatus can be used for the purpose of configuring complex protection functions. The use of the programmable display is illustrated with a simple example of under- impedance protection. Under-impedance protection is configured in an IED and is normally used as a backup protection for generators and transformers against short circuit faults. The IED calculates the impedance value from measured voltage and current quantities. The configuration sets up an operating region and if the impedance value decreases to such a value that it enters the operating region (less than the operating limit), the IED control mechanism triggers to operate after a preset time delay.

As an example, a system requiring under-impedance protection is illustrated in Figure 1. Figure 1 shows a network where under-impedance protection is used for protection of a generator 110. The generator 110 is connected to a step-up transformer 140. The under- impedance protection is set in an IED (Under impedance protection function) 120 to protect a zone 130 between the generator 110 winding and the generator side winding of the step-up transformer 140. For calculating impedance value, voltage and current values are required. The voltage is measured using instrument transformer 150 across the generatorl lO terminals and current flow is measured using instrument transformer 160 at the neutral point side of the generator 110.

The impedance is calculated using respective voltage and current phasors. Impedance value is calculated as the case maybe for single phase or multiple phase system using the formulas indicated below. For example for selected phases AB, U_AB is the voltage measured across the phases AB and I_A, I_B, are the currents measured in the phases of the generator. For selected phase AB, the impedance value is calculated as

The impedance values across different phase of the generator can be similarly calculated. The value of the impedance will be varying continuously with time. The magnitude of impedance is calculated continuously using the measured voltage and current values and when the value of impedance goes below the set value, the under-impedance protection starts. Thus, the preset value of the impedance defines the boundary for operating the under-impedance function. The threshold value preset by the user for the protection of the system as limiting region for impedance protection function is referred to as polar reach and is depicted on an R-X impedance plot 200 as shown in Figure 2 as an example of operating limit characteristics display.

For under-impedance protection the threshold is defined by the magnitude of the impedance known as polar reach 210 and is drawn as an origin centric circle with radius equal to the impedance (polar reach) as shown in Figure 2. The area of the circle indicates the operating region 230. The operating point 220 when enters into the operating region 230, the protection function is activated i.e. the operating region indicates the need for operation of the protection function. The operating value in this example is the impedance value of the system. Once the system is energized, the operating point of the system is shown on the screen for the operator. In one embodiment, the operating point is provided for the local HMI.

Apart from operating limit characteristics of the protection function, Figure 2 also indicates the current and voltage values for all three phases 240, in the example case for a three phase generator. Other information such as the threshold setting of the protection function characteristics or any other information which is necessary and is related to the characteristics function can be made available on the display.

During normal operating conditions the value of impedance is much higher than the threshold value and is said to be outside the operating limit (or in non-operating region). By changing the threshold value i.e. polar reach of the under-impedance protection function, the radius of the operating circle changes which further changes the operating region. Thus, by increasing the value of polar reach, the operating margin for under-impedance protection is reduced from the previously set value. This is illustrated in Figure 3. As it can be seen from Figure 3 , the initial operating region is the area of the circle with the radius as Polar reach_oi 210 and when the threshold value is increased from Polar reache_d 210 (initial polar reach as shown in the figure 2) to Polar reach_new 310 (shown in Figure 3) the operating region has increased to a larger area 320 with the radius of the circle as Polar reach_new. The characteristics boundary with new setting gets closer to operating point thus reducing the margin. Both the present and new proposed boundary limits due to changes in settings will be displayed on the screen; old boundary will be displayed for few seconds. The screen will help to visualize all these dynamic changes made to the system. The operating limit characteristics can be dynamically visualized i.e. the display will change as soon as user has made a change in the setting of the polar reach. Since, the device is calculating the impedance value to detect whether it is above or below threshold, the same value can also be displayed as an operating point on the characteristics plot. As the value of current and voltage in a system keeps on changing dynamically so is the impedance value. The dynamically changing impedance value is displayed and plot as an impedance locus on the operating limit characteristics. Further a feature can be added such that the dynamic movement of the point (locus of the point) is traced on the display. The traces may be managed appropriately to have an effective display of information for example a trace that contains data points which are old (may be >60 seconds) are deleted or the most recent trace point is shown brighter compared to the old data points which fade out gradually.

It may be noted that for the protection function, the protection parameters are measured or estimated based on measured values for comparison with associated threshold settings. Hence the information required to illustrate the operating point movement on an operating limit characteristics plot is readily available in a protection and control apparatus, which may be used for the creating an illustration or plot for the user. The illustration of an operating point on an operating limit characteristic is made using the under-impedance protection example as shown in Figure 4. Figure 4 provides an exemplary display that indicates the operating point movement, impedance value trajectory 410, from a value 220 in a normal region to a trip point 430 in an operating region 440. The display further may be useful to provide illustrations with example values of impedance at different instance of time. For example, At an instance of time tA 220, the calculated impedance is 60% of base impedance (Z_b), which is the ratio of the square of the base voltage to the base power which due to certain disturbance in the system is shown to decrease to 30% of Z_b, 420, at the instance of time tB, a point in the impedance value trajectory 410, and further shown to decrease to 10% of Z_b at the instance of time tc to a value shown at 430_. Thus, a change of the operating point at various instances can be dynamically observed by the user on the display and can effectively visualize the power system characteristics. The operating limit characteristics are depicted with polar reach 440 at a setting of 20% of Z_b. As the value of impedance at the instance of time tc has decreased below the setting of 20% of Z_b, which implies that the system has entered the operating region or protection limit, so the under-impedance protection gets activated after a preset delay. When the IED starts the protection function, the characteristics will pop-up for that function on the display. If more than one protection starts at the same time the pop-up may be in sequence or together or as per priority set by the user. Such illustration of operating point on the operating limit characteristic plots can be extended for protection functions such as thermal protection, distance protection, admittance protection, under-excitation protection, pole slip protection, differential protection, directional over and under power protection, directional overcurrent protection, directional earth fault protection, overcurrent protection, negative sequence overcurrent protection, over and under voltage protection etc.

The graphical display of such parameters is not limited to local HMI but can be made remotely as well. In an exemplary embodiment, a protection and control apparatus has a capability to calculate and compare the parameter for various protection purposes as these are primary functions. The apparatus in this embodiment has limited display capability, which includes a condition in a time, where the local display associated with the protection and control apparatus is not available under a particular condition that is determinable from the apparatus (eg computation load in the apparatus), the data as required for display of operating condition or setting is transmitted to a client station over a communication network connecting the protection and control apparatus and the client station. The client station provides the protection and control apparatus configuration and operating point for a function that is being observed, thus enabling remote display.

The display here is said to be made remotely available for e.g. in a control room or on a remote SCADA system. The information may also be retrieved on a web page to have a web enabled HMI i.e. a remote device can be a device that is on Internet to view web enable HMI. When such a data is displayed dynamically in a control room for all the protection functions and other interested functions, these functions and system operation, is under supervision of the control operators and acts as an excellent visualization tool indicating the boundary condition for operating protection function along with current system operating conditions which are difficult for visualization without such a graphical display.

Another exemplary use of the operating limit characteristics is to check the setting co-ordination i.e. where we have more than one instance of a particular protection function in a protection device or where more than one protection devices are incorporated and settings of protection functions are coordinated with each other.

An over current protection example is provided below illustrating three instances of overcurrent protection in a device for a radial outgoing feeder with an IED 510 at the output is shown in the Figure 5 . The basic requirement for a feeder overcurrent protection are adequate sensitivity and operating speed taking into account the minimum and maximum fault current, inrush current and the thermal withstand capacity of the line under protection. In most of the cases these requirements can be best fulfilled by using multiple stage of over current functions. Depending upon the value of the fault current, the apparatus will function.

The protection scheme is implemented with three stage overcurrent protection mechanism as shown in the figure 5, showing a typical characteristics plot having current (A) values in x axis and the time (s) values in y axis. The lower stage (3I>) 520 operates in inverse time mode and the high (3I») 530 and instantaneous (3I»>) stage 540 have definite time characteristics. Their purpose is to accelerate the operation of the protection under heavy fault current conditions. Also the thermal withstand 550 of the line and maximum expected inrush currents 560 of the feeder are shown. Faults occurring near the station where the fault current levels are highest are cleared rapidly by instantaneous stage in order to minimize the effects of short circuit faults. The influence of inrush current is taken into consideration by connecting the inrush current detector to a start value multiplying input of instantaneous stage. The system also shows the essential parameters like the maximum load 580 current and the rated current 590 of the current feeder.

The display (local or remote) can depict the information in a collective manner to assist a user to understand how the setting is made for all the instances, whether the required time grading between all the three instances are provided. Such collective information may also be gathered when more than one protection and control apparatus is being used, through exchange of data in a communication network connecting the multiple protection and control apparatus and clients for display when remote display is opted to check and have proper co-ordination plan (selectivity diagram) for the overall system.

The selectivity diagram is a set of specific time-current curves which shows all the time- current curves, i.e. operating characteristics of protection devices. The chain of protective device in Figure 6 includes two protection devices. The selectivity diagram also includes additional information needed for planning and operation of protection such as lowest and highest fault current levels in the relaying points, maximum load current, nominal current and maximum limit values of possible inrush currents etc.

The exemplary system with the following protection design with two protection devices (Device 1 610 and Device 2 620) to protect an incoming and an outgoing feeder is used to illustrate the use of graphical operating limit characteristics information. The system is such that if a fault happens, say in the far end of the outgoing feeder, it is protected by the first protection device 610 (Device 1). The second protection device 620 (Device 2) is connected at the incoming feeder. The fault current magnitude at fault is said to be of the level indicated by 630. This fault causes both protection device 1 (610) and device 2 (620) to start, with device 2 (620) providing an inherent backup protection for the feeder. Should device 1 or the circuit breaker associated with the outgoing feeder fail to operate, device 2 should be allowed to operate. The collective information of settings (635, 637) from Device 1 and Device 2 are depicted together in Figure 6 where the coordination design may be visually appreciated. The maximum load current value (outgoing) depicted with numeral 640, the maximum load current value (incoming) depicted with numeral 645 and the rated line current (incoming) 650 can be suitably represented in the display. Further, the inrush current limit 655, thermal capacity of outgoing feeder, 660 and the thermal capacity of incomer, 665 are also represented in the display.

Thus by getting design and setting characteristics of different device and overlapping them it is possible to check and see whether appropriate selectivity is obtained or not. Also as the display is dynamic in case if someone changes the settings, it is possible to visualize the changes made and any if there are any incorrect setting which distorts the coordination, those may be notified by the system and can be rectified as a result to avoid any mal operation caused by improper settings.

Minimum capability can be provided within a device, in an embodiment, providing coordination in the device under consideration with (a) one such device located downstream and with (b) one such device located upstream depending upon the capability of the device under consideration and complexity of the system. It may be possible to transfer the values and carry out this display functionality totally in the SCADA system and later used to configure involved devices appropriately.

Figure 7 provides a block diagram for a protection and control apparatus 700 in an electrical subsystem. The block diagram represents some of the functions involved in providing a dynamic display in the protection and control apparatus (IED). The IED has a base unit 790 for monitoring and control functions that is a general protection and control apparatus. Signal parameters 710 are received from the system and these could be any signal such as voltage, current, temperature, pressure etc., which are received from a field device such as sensor or instrument transformer, obtained through a hardwire or wireless connection, as analog signal or digital information. The apparatus has a signal interface 720 which can contain hardware or firmware circuits for filtering, noise reduction /removal, sampling and any signal interface hardware for input or signal processing circuitry needed for capturing and processing of analog input or digital information as the case maybe. A protection block having a suitable protection algorithm is depicted in 730 that can be executed in a programmable controller having a memory, depicted in a block represented by 750. The controller determines a condition for issuing a trip signal 760 by comparing values from measurement or computation with a preset threshold values in the IED.

The controller can be a processor that is a combination of hardware and software which takes current and voltage input and calculated various quantities likes RMS value, DFT value, peak-to- peak value, various harmonics, frequency, angle w.r.t. reference etc. for each sampled analog channel and applied for suitable computation using protection algorithms. Any of the block illustrated in the figure may be based on or prepared through use of programmable devices or blocks eg Field Programmable Gate Array (FPGA).

In one embodiment, the IED has a HMI unit 765 for display and to receive input configurations. The HMI unit or block can be an integral part of the IED or can be an attachable part to the IED. The measured, computed and configured values related to one or more protection functions are provided by the base unit 790 to the HMI block 765 for display. The HMI block has a HMI (graphical user interface), 770 that can be an integrated display and input device such as a touch screen with a suitable display or a separate display and input device (eg switches). Additionally, the input configuration may also be obtained through a programmable interface or as a configuration from a programmable system connecting the IED (or the HMI block) with the programmable system through a communication channel (785). The communication channel can also be used to connect multiple IEDs in the system for coordination and sharing of information. The communication channel can be the same channel through with the base unit communicates in the electrical subsystem The HMI block 765 can have a separate controller and memory 780 to process and configure display for displaying operating limit characteristics as described in examples earlier. Thus, the HMI block offers a programmable display.

Apart from the display the HMI block 765 can support various user friendly features like zoom, touch screen etc, managed with the help of controller and memory block 780. The HMI block can also have recording facility which records the trend of the locus movement if needed (to record locus of few millisecond of pre-fault and post data for fault analysis). Thus, additional features related to display and management of information can be provided without burdening the IED block 790 configured primarily for control and protection functions.

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

Claims:

1. A method for displaying operating limit characteristics of an electrical subsystem in a power system, on a graphical user interface of an Intelligent Electronic Device (IED), the method comprising the steps of:

having an operating limit value configured for a protection function in the IED;

calculating an operating region from the configured operating limit value in the IED;

measuring at least one signal parameter from the electrical subsystem in the power system; calculating an operating point value for the protection function from the at least one measured signal parameter; and

displaying the operating region along with the operating point value on the graphical user interface of the IED.

2. The method of claim 1, wherein the step of displaying the operating point value comprises tracing the movement of the operating point value on the graphical user interface.

3. The method of claim 1, wherein the step of displaying the operating region comprises of displaying a first operating region corresponding to a first configured operating limit value along with displaying of a second operating region corresponding to a second configured operating limit value.

4. The method of claim 3, wherein displaying the first operating region corresponding to the first configured operating limit value along with displaying of a second operating region corresponding to the second configured operating limit value that is obtained from one or more remote device in the power system.

5. An intelligent electronics device (IED) for protection and control function in an electrical subsystem in a power system comprising of:

a base unit for measuring and processing at least one signal parameter in the electrical subsystem and generate a trip signal derived from comparison with an operating limit value provided in the IED; and a human machine interface (HMI) unit for displaying an operating point value derived from the at least one signal parameters and for displaying an operating region derived from the operating limit value provided in the IED.

6. The IED of claim 5, wherein the said at least one signal parameter received in the electrical subsystem includes electrical or physical signal.

7. The IED of claim 5, wherein the human machine interface unit displays dynamic behavior of an operating point value along with an operating region.

8. The IED of claim 5, wherein the human machine interface unit displays an operating point value or an operating region derived from an operating limit value provided in the IED from a remote device.

9. The IED of claim 5, wherein the IED is capable to provide an operating point value or an operating limit value to a remote device in the electrical subsystem and wherein the remote device is a client station or another IED with a HMI unit or a device on Internet.

10. The IED of claim 5, wherein the HMI unit in the IED is used for configuring an operating limit value in the IED for coordinating protection in an electrical subsystem or for recording dynamic behavior of an operating point value in the IED.