PCS 994s x technical manual EN overseas general x r1 00

Preface About This Manual The technical manual describes the protection, automation, control, and supervision functions of PCS S series device for line differential protection, and cont

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To the extent required the products described herein meet applicable IEC and IEEE standards, but no such assurance is given with respect to local codes and ordinances because they vary greatly

Although every reasonable effort is made to present current and accurate information, this document does not purport to cover all details or variations in equipment nor provide for every possible contingency to be met in connection with installation, operation, or maintenance Should further information be desired or should particular problems arise which are not covered sufficiently for your purposes, please do not hesitate to contact us

Preface

About This Manual

The technical manual describes the protection, automation, control, and supervision functions of PCS S series device for line differential protection, and contains operation principle descriptions, and lists function blocks, logic diagrams, input and output signals, setting parameters and technical data, sorted per function, as well as the hardware of the device The manual can be used as a technical reference during the engineering phase and during normal service In addition, the manual also includes a glossary that lists and defines technical terms used throughout the manual

Safety Information

This manual is not a complete index of all safety measures required for operation of the equipment (module or device) However, it comprises important information that must be followed for personal safety, as well as to avoid material damage Information is highlighted and illustrated

as follows according to the degree of danger:

Indicates an imminently hazardous situation that, if not avoided, will result in death or serious injury

Indicates a potentially hazardous situation that, if not avoided, could result in death or serious injury

Indicates a potentially hazardous situation that, if not avoided, may result

in minor or moderate injury or equipment damage

Indicates that property damage can result if the measures specified are

not taken

Important information about the device, product handling or a certain section of the documentation which must be given particular attention

Instructions and Warnings

The following hazard statements apply to this device

Disconnect or de-energize all external connections BEFORE opening this

device Contact with hazardous voltages and currents inside this device can cause electrical shock resulting in injury or death

Contact with instrument terminals can cause electrical shock that can result in injury or death

Use of this equipment in a manner other than specified in this manual can impair operator safety safeguards provided by this equipment

Have only qualified personnel service this equipment If you are not qualified to service this equipment, you can injure yourself or others, or cause equipment damage

This device is shipped with default passwords Default passwords should

be changed to private passwords at installation Failure to change each default password to a private password may allow unauthorized access

NR shall not be responsible for any damage resulting from unauthorized access

DO NOT look into the fiber (laser) ports/connectors

DO NOT look into the end of an optical cable connected to an optical

output

DO NOT perform any procedures or adjustments that this instruction

manual does not describe

During installation, maintenance, or testing of the optical ports, ONLY use

the test equipment qualified for Class 1 laser products!

Incorporated components, such as LEDs, transceivers, and laser emitters,

are NOT user serviceable Return units to NR for repair or replacement

Equipment components are SENSITIVE to electrostatic discharge (ESD)

Undetectable permanent damage can result if you do not use proper ESD procedures Ground yourself, your work surface, and this equipment

BEFORE removing any cover from this equipment If your facility is not

equipped to work with these components, contact NR about returning this device and related NR equipment for service

Insufficiently rated insulation can deteriorate under abnormal operating conditions and cause equipment damage For external circuits, use wiring

of SUFFICIENTLY RATED insulation that will not break down under

abnormal operating conditions

SEVERE power and ground problems can occur on the communications

ports of this equipment as a result of using non-standard cables Please use the wiring method recommended in the manual for communication terminals

DO NOT connect power to the relay until you have completed these

procedures and receive instruction to apply power Equipment damage can result otherwise

Use of controls or adjustments, or performance of procedures other than

those specified herein, may RESULT IN hazardous radiation exposure

The firmware may be upgraded to add new features or enhance/modify

existing features, please MAKE SURE that the version of this manual is

compatible with the product in your hand

Document Conventions

 The abbreviations and acronyms in this manual are explained in “Appendix A Glossary” The

Glossary also contains definitions of important terms

 Menu path is connected with the arrow "→" and bold

For example: the access path of protection settings is: MainMenu→Settings→Protection Settings

 Settings not in the table should be placed in brackets

For example: the system setting [Opt_SysFreq]

 Cross-references are presented in italics

For example: refer to Figure 1.1-1, refer to Table 1.1-1, reference to Section 1.1

 Binary input signals, binary output signals, analogs, LED lights, buttons, and other fixed meanings, should be written in double quotes and bold

For example: press the button "ENT"

on the target sections of this manual as your job needs and responsibilities dictate An overview of each manual section and section topics follows

6 System Functions

Describes how to perform fundamental operations such as clock synchronization, communicating with the device, switching active setting group, checking relay status, reading event reports and SER (Sequential Events Recorder) records

Describes the abbreviations adopted in this manual

Document Revision History

PN: ZL_PCS-994S_X_Technical Manual_EN_Overseas General_X

Figure 1.1-1 Typical applications of PCS-994S 1-1

Figure 1.1-2 Function diagram of PCS-994S 1-1

1

1.1 Application

PCS-994S frequency and voltage controller provides fast and selective generation shedding and

load shedding due to the frequency or voltage abnormality in the power network, for avoiding the

system crash and a large area blackout, maintaining the stability of the system voltage and

frequency The device contains all important auxiliary functions that are necessary today for safe

network operation This includes measurement and monitoring functions The large number of

communication interfaces and communication protocols satisfies the requirements of

communication-based selective control and of automated operation Their modular structure

permits the device always to be adapted flexibly to the individual requirements

PCS-994S applies to double-bus scenarios and single bus with bus section scenarios

PCS-994S

Bus1 Bus2

PCS-994S

Figure 1.1-1 Typical applications of PCS-994S

The function diagram for protecting a double-bus is shown below

Figure 1.1-2 Function diagram of PCS-994S

The PCS-994S is applicable not only to conventional substations, but also to digital substations It

supports IEC 61850 Editions 1 and 2 and provides GOOSE and SV network interfaces with high

real-time performance The process level network supports peer-to-peer (P2P) mode and

networking mode, including single network mode and dual network mode The station level

network could also receive and send MMS messages (such as interlocking signals) or process

level GOOSE messages (such as trip signals)

1

1.2 Functions

1 Protection Functions

81U Under-frequency protection

 Up to 5 basic stage of under-frequency load shedding

 Up to 2 accelerated stage of under-frequency load shedding

 Up to 3 special stage of under-frequency load shedding

 Under-voltage blocking element

 df/dt blocking element

 Frequency over-range blocking element

81O Over-frequency protection

 Up to 5 basic stage of over-frequency generation shedding

 Under-voltage blocking element

 Frequency over-range blocking element

81R Rate-of-change of frequency

protection

 Up to 5 stages with independent logic

 Optional positive or negative change of frequency for each stage

 Under-voltage blocking element

27 Under-voltage protection

 Up to 5 basic stage of under-voltage load shedding

 Up to 2 accelerated stage of under-voltage load shedding

 Up to 3 special stage of under-voltage load shedding

 Under-voltage blocking element

 dU/dt blocking element

 VT circuit failure blocking

59 Over-voltage protection  Up to 3 basic stage of over-voltage system splitting

2 Measurement and Metering Functions

 Powerful faults recording (max buffer for 10,000 sampled points at 4.8 or 9.6 kHz

 Event Recorder including 1024 disturbance records, 1024 binary events, 1024 supervision events, 256 control logs and 1024 device logs

 Disturbance recorder including 64 disturbance records with waveforms (The file format of disturbance recorder is compatible with international COMTRADE file.)

1

 Single line diagram representation in display

4 Communication Functions

 Support of various protocols

Modbus, DNP3.0, IEC 60870-5-103, IEC 61850 Ed.1 & Ed.2, IEC 61850 MMS Server,

IEC 61850-8-1 GOOSE, IEC 61850-9-2LE SV, IEC 62439 Parallel Redundancy Protocol,

IEC 62439 HSR Ring Redundancy Protocol

 Up to four 10Base-T/100Base-TX copper Ethernet ports

 Up to four 100Base-FX optical Ethernet ports

 Two RS-485 serial ports for communication or printer

 One RS-485/TTL/ST port for clock synchronization

 Two RJ45 debugging ports (front and rear)

5 User Interfaces

 Friendly HMI interface with LCD, easy-to-use keypad aids simple navigation and

set-point adjustment

 Push buttons for open/close, switch for selection between local and remote control, and

user's login and logout authority management

 4 Programmable operator pushbuttons with user-configurable labels

 Up to 18 programmable target LEDs with user-configurable labels

 1 RS-485 rear port for printer

 Language switchover—English+ selected language

 Configuration tool—PCS-Studio

6 Additional Functions

 User programmable logic

 Switching system phase sequences function (ABC or ACB)

 Clock synchronization

 IRIG-B: IRIG-B via RS-485 differential level, TTL level or optical fibre interface

 PPS: Pulse per second (PPS) via RS-485 differential level or binary input

 PPM: Pulse per minute (PPM) via RS-485 differential level or binary input

 IEEE1588: Clock message based on IEEE1588 via optical fibre interface

 SNTP (PTP): Unicast (point-to-point) SNTP mode via Ethernet network

 SNTP (BC): Broadcast SNTP mode via Ethernet network

 Various function modules can satisfy various situations according to the different requirements

of users Flexible and universal logic programming, user-defined configuration of BI/BOs, buttons and LEDs and powerful analog programming are supported

 Modularized hardware design makes the device be easily upgraded or repaired by a qualified service person It can be mixed with different I/O modules, with online self-check and monitoring function, and the device can be restored from abnormal operation only need to replace a single abnormal module

 Support memory check and error correction function, ensure high reliability and safety

 Support the internet communication protocol of native PRP/HSR and RSTP

 Fully compatible with IEC 61850 edition 1 & edition 2, support MMS service, IEC 62351 communication service, GOOSE communication in station level & process level, SV communication with multi-sampling rate

 Full comply with cyber security standards, including IEC62443, IEC62351, IEEE1686, NERC-CIP, support role based access control (RBAC), security audit, security encryption communication and security tool, improve the cyber security capability of devices

 Powerful COMTRADE fault and disturbance recording function is supported The whole recording time is automatically configurable by the fault duration, which is convenient to fault analysis and replay The recording sample rate is up to 9.6kHz

 Settable secondary rated current (1A/5A) and settable voltage threshold of binary input

1

 Support small size and large size LCD, control and multifunction button

 Support flush mounting, semi-flush mounting, surface mounting, wall mounting and other

mounting methods

 Cross screw IO, CT/VT terminals can support AWG12 specification connector and 4mm2

lead

 Multiple variants with case size 1/1 or 1/2 × 19"

 Protection class of front side is up to IP54

 PCS-Studio is the application software on the user's PC for the interface with PCS S series

devices providing all the related functionality It ranges from device configuration to full

substation design of bay integration

 Support IEEE1588, IRIG-B clock synchronization

 Support actual system phase sequence, either ABC or ACB, incorrect connection of actual

phase sequence can automatically be verified and relevant protection functions can be

blocked

 Equipped with high-speed large capacity output relay, its operation speed is less than 1ms and

its break capacity is up to 10A The real-time supervision for output drive circuit can detect the

abnormality in advance

 Support setup up to 40 users and allow each user to own different password and access

authority

 The PCS-994S can accelerated load shedding to prevent power system collapse when the

system’s voltage or the frequency decreases sharply Thus, the voltage or frequency can be

restored back to optimal operating range quickly

 Since the decrease of three-phase voltage due to insufficient reactive power is basically

symmetric, and no large sudden variation occurs, the under-voltage element of this controller

makes judgments based on positive-sequence voltage If a negative-sequence voltage

exceeds 0.15Un or a positive-sequence voltage changes suddenly, the under-voltage load

shedding function is blocked Therefore, the controller will not execute system-splitting during

faults

 The power swing blocking function, based on the analysis of df/dt and du/dt, can prevent

mal-operation caused by short-circuit fault or abnormal conditions of voltage and frequency

 The adaptive floating threshold method is adopted, which only reflects the frequency

component deviation of power supply This measuring element improves the protection

sensitivity and stability under load fluctuation and system disturbance conditions

 Unique two-out-two logic is adopted in the hardware design to improve security, while the

redundant scheme improves dependability The two independent data acquisition channels

are provided to prevent mal-operation caused by component failure One works as a fault

detector and the other is designed for protection logic

2.11 Communication Functions 2-11

2.11.1 GOOSE 2-11 2.11.2 SV 2-12 2.11.3 IEC61850-9-2 Transmission Parameters 2-12 2.11.4 Sampled Value Accuracy 2-12

2

2.1 Electrical Specifications

“System phase sequence”, which can be set by PCS-Studio, this setting

informs the device of the actual system phase sequence, either ABC or ACB VT inputs on the device, labeled as A, B and C, must be connected

to system phase A, B and C for correct operation

600V 660V

Phase-to-phase 519V

1038V 1141V

Burden at rated <0.10VA/phase @100V

2.1.2 Power Supply

100Vac/110Vac/115Vac/120Vac 127Vac/220Vac/230Vac/240Vac 250Vac

Permissible AC ripple voltage ≤15% of the nominal auxiliary voltage

2

Settable pickup voltage and dropout voltage

On value (default set) 69.3~132Vdc 78.75~160Vdc 138.6~264Vdc 157.5~300Vdc

Off value (default set) <55Vdc <62.5Vdc <110Vdc <125Vdc

Maximum permissible voltage 300Vdc

Withstand voltage 2000Vac, 2800Vdc (continuously)

Settable pickup voltage and dropout voltage

Maximum permissible voltage 300Vac

Withstand voltage 2000Vac, 2800Vdc (continuously)

Settable pickup voltage and dropout voltage

Maximum permissible voltage 300Vdc

Withstand voltage 2000Vac, 2800Vdc (continuously)

2.1.4 Binary Output

Tripping/signaling contact

Max system voltage 250Vac, 300Vdc

Pickup time (Typical value) <5ms

2

Dropout time (Resistive load) <6ms

Breaking capacity (L/R=40ms)

0.5A@48Vdc 0.35A@110Vdc 0.30A@125Vdc 0.20A@220Vdc 0.15A@250Vdc

Cyclic Capacity (2.5 cycle/second,

L/R=40ms)

0.5A@48Vdc 0.35A@110Vdc 0.30A@125Vdc 0.20A@220Vdc 0.15A@250Vdc

Short duration current

30A@3s 50A@1s Durability (Loaded contact) 10000 operations

Heavy-capacity tripping contact

MOV Protection (maximum voltage ) 350Vdc, 275Vac

Pickup time (Typical value) <1ms

Dropout time (Resistive load) <10ms

Breaking capacity (L/R=40ms)

10A@48V 10A@110V 10A@125V 10A@250V

Cyclic Capacity (4 cycles in 1 second,

followed by 2 minutes idle for thermal

dissipation)

10A@48V L/R=40ms 10A@110V L/R=40ms 10A@125V L/R=40ms 10A@250V L/R=20ms

2

Short duration current

30A@3s 50A@1s Durability (Loaded contact) 10000 operations

2.2 Mechanical Specifications

Weight per device

Approx 5.86kg (6U, 1/2) Approx 9.22kg (6U, 1/1)

Location of terminal Rear panel of the device

Device structure Plug-in modular type @ rear side, integrated front plate

Protection Class

Rear side, connection terminals IP20

2.3 Ambient Temperature and Humidity Range

2

Max transmission distance 500m

Safety level Isolation to ELV level

Twisted pair Screened twisted pair cable

2.4.2 Copper Ethernet Port

Transmission standard 100Base-TX

Max transmission distance 100m

Protocol IEC 60870-5-103:1997, DNP 3.0 or IEC 61850

Safety level Isolation to ELV level

2.4.3 Optical Port

Optical Port: For Station Level and Process Level

Characteristic Glass optical fiber

Transmission distance Maximum 2km

Transmission power 50μm: Minimum -24dBm 62.5μm: Minimum -20dBm

Optical Port: For Clock Synchronization

Characteristic Glass optical fiber

2

Peak optical input power

Logic level HIGH

Logic level LOW

Maximum -40dBm Maximum -10dBm, Minimum -24dBm

2.4.4 Print Port

Baud Rate 4.8kbit/s, 9.6kbit/s, 19.2kbit/s, 38.4kbit/s, 57.6kbit/s, 115.2kbit/s

Safety level Isolation to ELV level

2.4.5 Clock Synchronization Port

Damp heat test, cyclic IEC60068-2-30:2005

2.5.2 Mechanical Tests

Shock and bump IEC 60255-21-2:1988 Class Ⅰ

2.5.3 Electrical Tests

Dielectric tests Test voltage 2kV, 50Hz, 1min

Electrostatic discharge test

IEC 61000-4-2-2008 class Ⅳ For contact discharge: 8kV For air discharge: 15kV

Radio frequency interference tests

IEC 60255-26:2013 class Ⅲ Frequency sweep

Radiated amplitude-modulated 10V/m (rms), f=80~1000MHz, 14000~2700MHz Spot frequency

Radiated amplitude-modulated 10V/m (rms), f=80MHz/160MHz/450MHz/900MHz

Fast transient disturbance tests

IEC 60255-26:2013 Power supply, I/O, Earth: class Ⅳ, 4kV, 5kHz, 5/50ns Communication terminals: class Ⅳ, 2kV, 5kHz, 5/50ns

Surge immunity test

IEC 60255-26:2013 Power supply, AC input, I/O port: class Ⅳ, 1.2/50us Common mode: 4kV

Differential mode: 2kV

Conducted RF Electromagnetic

Disturbance

IEC 60255-26:2013 Power supply, AC, I/O, Comm Terminal: Class Ⅲ , 10Vrms, 150 kHz~80MHz

Spot frequency

2

10V/m (rms), f=27MHz/68MHz Power Frequency Magnetic Field

Immunity

IEC 61000-4-8: 2009 class Ⅴ, 100A/m for 1min, 1000A/m for 3s

Pulse Magnetic Field Immunity

IEC 61000-4-9:2016 class Ⅴ, 6.4/16μs, 1000A/m for 3s Damped oscillatory magnetic field

immunity

IEC 61000-4-10:2016 class Ⅴ, 100kHz & 1MHz–100A/m

Conducted emission

IEC 60255-26:2013 0.15MHz~0.50MHz: 79dB (μV) quasi peak, 66dB (μV) average 0.50MHz~30MHz: 73dB (μV) quasi peak, 60dB (μV) average

Radiated emission

IEC 60255-26:2013

Below 1GHz

30MHz~230MHz: 40dB (μV/m) quasi peak @10m, 50dB (μV/m) quasi peak @3m

230MHz~1000MHz: 47dB (μV/m) quasi peak @10m, 57dB (μV/m) quasi peak @3m

Above 1GHz

1GHz~3GHz: 56dB (μV/m) average, 76dB (μV/m) peak @3m

3GHz~6GHz: 60dB (μV/m) average, 80dB (μV/m) peak @3m

Auxiliary power supply performance

50ms for interruption without rebooting without energy storage board (Typical configuration) 500ms for interruption without rebooting with energy storage board (Typical configuration)

2.6 Certifications

 ISO9001:2015

 EMC: 2014/30/EU, EN60255-26:2013

 Products safety (LVD): 2014/35/EU, EN60255-27:2014

 IEC 61850: Edition 2, Parts 6, 7-1, 7-2, 7-3,7-4 and 8-1

 IEC 61850: Edition 2, GOOSE Performance Class P1 (3ms)

 IEEE 1588: IEEE Std C37.238TM-2017

 DNP: DNP 3.0

 PRP: IEC 62439-3 Ed.3 (IS 2016)

 HSR: IEC 62439-3 Ed.3 (IS 2016)

2.7 Liquid Crystal Display (LCD)

2.8 Terminals

2.8.1 Ring Ferrule

Grounding (Earthing) Connection BVR type, 0.8~4mm2 lead M3 0.6~0.8 N·m

2.8.2 Pin Ferrule

Power supply Screw terminals, 0.3~3.3mm2 lead M2.5 0.4~0.6 N·m

Contact I/O Screw terminals, 0.3~3.3mm2 lead M2.5 0.4~0.6 N·m

External time synchronization IRIG-B (200-98), PPS, IEEE1588 or SNTP protocol

2.9.2 Fault and Disturbance Recording

Duration & Recording position

Settable pre-disturbance, post-disturbance and maximum recorded duration

2.9.3 Binary Input Signal

Resolution of binary input signal ≤1ms

2.10 Protective Functions

2.10.1 Under-frequency Protection (81U)

Tolerance of frequency setting ≤0.01Hz

Tolerance of operating time ≤1%×setting or 60ms

2.10.2 Over-frequency Protection (81O)

Tolerance of frequency setting ≤0.01Hz

Tolerance of operating time ≤1%×setting or 60ms

2

2.10.3 Frequency Rate-of-change Protection (81R)

Tolerance of frequency rate-of-change setting ≤0.02Hz/s

Tolerance of operating time ≤1%×setting or 60ms

2.10.4 Under-voltage Protection (27)

Tolerance of voltage setting ≤1.5% or 0.1V, whichever is greater

Tolerance of operating time ≤1%×setting or 30ms

2.10.5 Over-voltage Protection (59)

Tolerance of voltage setting ≤1.5% or 0.1V, whichever is greater

Tolerance of operating time ≤1%×setting or 30ms

Sending Control Block (SCB) Max 16

2

2.11.2 SV

Receiving Control Block (RCB) Max 12

2.11.3 IEC61850-9-2 Transmission Parameters

Transmission frame interval jitter < 300ns

2.11.4 Sampled Value Accuracy

Voltage accuracy for measurement

Accuracy class 0.2 class Amplitude (Typical) < 0.1% @ Un Angle (Typical) < 5’ @ Un

Voltage accuracy for protection

Amplitude (Typical) < 0.1% @ Un Angle (Typical) < 5’ @ Un

3

3.5.1 Function Description 3-22 3.5.2 Function Block Diagram 3-23 3.5.3 I/O Signal 3-23 3.5.4 Logic 3-23 3.5.5 Settings 3-23

List of Figures

Figure 3.1-1 Logic diagram of load over-shedding by stage 2 of under-frequency protection 3-4 Figure 3.1-2 Function block of basic stages of under-frequency protection 3-4 Figure 3.1-3 Function block of accelerated stages of under-frequency protection 3-4 Figure 3.1-4 Function block of special stages of under-frequency protection 3-4 Figure 3.1-5 Logic of basic stages of under-frequency protection 3-5 Figure 3.1-6 Logic of accelerated stages of under-frequency protection 3-6 Figure 3.1-7 Logic of special stages of under-frequency protection 3-6 Figure 3.2-1 Logic of over-frequency protection 3-11 Figure 3.3-1 Logic of frequency rate-of-change protection 3-13 Figure 3.4-1 Schematic of blocking and unblocking upon short circuit 3-17 Figure 3.4-2 Function block of basic stages of under-voltage protection 3-17 Figure 3.4-3 Function block of accelerated stages of under-voltage protection 3-18 Figure 3.4-4 Function block of special stages of under-voltage protection 3-18 Figure 3.4-5 Logic of basic stages of under-voltage protection 3-19 Figure 3.4-6 Logic of accelerated stages of under-voltage protection 3-19 Figure 3.4-7 Logic of special stages of under-voltage protection 3-20 Figure 3.5-1 Logic of over-voltage protection 3-23

List of Tables

Table 3.1-1 I/O signals of basic stages of under-frequency protection 3-5 Table 3.1-2 I/O signals of accelerated stages of under-frequency protection 3-5 Table 3.1-3 I/O signals of special stages of under-frequency protection 3-5

3

Table 3.1-4 Settings of under-frequency protection 3-7

Table 3.2-1 I/O signals of over-frequency protection 3-10

Table 3.2-2 Settings of over-frequency protection 3-11

Table 3.3-1 I/O signals of frequency rate-of-change protection 3-13

Table 3.3-2 Settings of frequency rate-of-change protection 3-13

Table 3.4-1 I/O signals of basic stages of under-voltage protection 3-18

Table 3.4-2 I/O signals of accelerated stages of under-voltage protection 3-18

Table 3.4-3 I/O signals of special stages of under-voltage protection 3-18

Table 3.4-4 Settings of under-voltage protection 3-20

Table 3.5-1 I/O signals of over-voltage protection 3-23

Table 3.5-2 Settings of over-voltage protection 3-23

3

3.1 Under-frequency Protection (81U)

Frequency is an important index of the power quality, which can reflect the balance of the output

power of the generator and the active power of the load The decrease of frequency indicates that

the output power of the system is much less than that of the load When the system frequency is

less than the predefined setting, the under-frequency protection will operate for shedding some

part of loads from the system

3.1.1 Function Description

The device can provide five basic stages, two accelerated stage, and three special stages of

under-frequency load shedding If the system frequency is less than the setting, under-frequency

protection will operate to shedding some part of loads from the system Under-frequency

protection is with definite-time characteristics and with instantaneous dropout characteristics

3.1.1.1 Discriminated Equations of Under-frequency Load Shedding

There are two kinds of operation sequences for basic stages, independent and sequential

 For the logic that the five basic stages operate independently, the discriminated equations

are,

When f≤ f_Pkp_UF & t≥0.05s FD (fault detector) of under-frequency protection will pick up,

then

If f≤[81U1.f_Set] & t≥[81U1.t_Op], basic stage 1 of under-frequency will operate;

If f≤[81U2.f_Set] & t≥[81U2.t_Op], basic stage 2 of under-frequency will operate;

If f≤[81U3.f_Set] & t≥[81U3.t_Op], basic stage 3 of under-frequency will operate;

If f≤[81U4.f_Set] & t≥[81U4.t_Op], basic stage 4 of under-frequency will operate;

If f≤[81U5.f_Set] & t≥[81U5.t_Op], basic stage 5 of under-frequency will operate

(Where, f is the frequency of the selected voltage, f_Pkp_UF is the internal pickup setting, it

follows the rule as below:

If [81U.f_Pkp]≠0.00Hz, f_Pkp_UF = [81U.f_Pkp], where [81U.f_Pkp] is the under-frequency

pick up setting;

Else if [81U.f_Pkp]=0.00Hz, f_Pkp_UF=MAX{[81U1.f_Set], [81U2.f_Set]… [81U5.f_Set]…

[81US3.f_Set]} + 0.1Hz, t is the time delay)

 For the logic that the five basic stages operate sequentially, the discriminated equations are,

When f≤f_Pkp_UF & t≥0.05s fault detector of under-frequency protection will pick up, then

If f≤[81U1.f_Set] & t≥[81U1.t_Op], basic stage 1 of under-frequency will operate

↓ if f≤[81U2.f_Set] & t≥[81U2.t_Op], basic stage 2 of under-frequency will operate

↓ if f≤[81U3.f_Set] & t≥[81U3.t_Op], basic stage 3 of under-frequency will operate

3

↓ if f≤[81U4.f_Set] & t≥[81U4.t_Op], basic stage 4 of under-frequency will operate

↓ if f≤[81U5.f_Set] & t≥[81U5.t_Op], basic stage 5 of under-frequency will operate (Where, “↓” means the above conditions have been met and realized.)

The discriminated equations of the two accelerated stages are shown as below

When f≤[f_Pkp_UF] & t≥0.05s fault detector of under-frequency protection will pick up, then

If f≤[81U1.f_Set] & {[81UAcc2.df/dt_Set]≤－df/dt＜[81U.df/dt_H_Blk]} & t≥[81UAcc2.t_Op], stage 1 of under-frequency will trip and stage 2 will be accelerated to trip

If f≤[81U1.f_Set] & {[81UAcc2-3.df/dt_Set]≤ － df/dt ＜ [81U.df/dt_H_Blk]} & t≥[81UAcc2-3.t_Op], stage 1 of under-frequency will trip, and stage 2 and stage 3 will be accelerated to trip

The discriminated equations of the three special stages are shown as below

When f≤f_Pkp_UF & t≥0.05s fault detector of under-frequency protection will pick up, then

If f≤[81US1.f_Set] & t≥[81US1.t_Op], special stage 1 of under-frequency will operate

If f≤[81US2.f_Set] & t≥[81US2.t_Op], special stage 2 of under-frequency will operate

If f≤[81US3.f_Set] & t≥[81US3.t_Op], special stage 3 of under-frequency will operate

3.1.1.2 Blocking Measures to Prevent Maloperation

In order to prevent possible device maloperation in conditions of high harmonics, voltage circuit failure and so on, such blocking measures are carried out as follows:

1 Voltage control element (under-voltage blocking)

If the positive voltage U1<[81.U_VCE] (the under-voltage blocking setting), the under-frequency protection will be blocked

2 df/dt blocking element

If －df/dt ≥ [81U.df/dt_H_Blk], the under-frequency protection will be blocked The df/dt blocking effect will be released automatically until the system frequency returns to be greater than the pickup setting of under-frequency load shedding

3 Frequency over-range blocking element

When any one of the following inequality is met, the device will take the system frequency as abnormality

For the 50Hz system, f<33Hz or f>65Hz

For the 60Hz system, f<40Hz or f>72Hz

In parallel operation condition, if the device detect that the system frequency calculated from one bus voltage is abnormal or the voltage is close to zero, it will switch over-voltage sampling source

to the other bus; if the voltages of both buses are all detected to be close to zero or both of the