RTU training ILSAS1

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Jabatan Kejuruteraan (Telekontrol) -Dec 2005Bahagian Penghantaran

Firdaus Yon Institut Latihan Sultan Ahmad Shah(ILSAS)

Pengenalan

• Memenuhi salah satu syarat sijilkompetensi telekontrol

• Mengulangkaji/Memperkukuhkan

pengetahuan dan kemahiran yg perlu utkmenyelia dan menjalankan kerja-kerja

telekontrol di pencawang





Objektif

• Di akhir kursus, peserta akan boleh: - – Mengenali semua peralatan telekontrol di

pencawang dan alat-alat ujian telekontrol

– Menjalankan pemasangan dan mulatugas alat

telekontrol dan SCS untuk pencawang baru

dan tambahan

– Menjalankan penyelenggaraan alat telekontrol

dan SCS di pencawang – Menjalankan kerja-kerja baikpulih ke atas alat

telekontrol dan SCS





Penilaian

• Salah satu syarat sijil kompetensiTelekontrol

• Kategori Penilaian

– Quiz untuk setiap topik – Workshop

– Ujian Akhir Kursus

• Kelayakan – Prestasi memuaskan untuk setiap kategori

penilaian (minima 60%)





Peringatan

• Ulangkaji• Skop luas – banyak topik.

• Masa singkat – perbincangan yang

mendalam mengenai topik-topiksimpangan mungkin tidak dapat dijalankan

• May extend lecture hours. All topics must

be covered.





Program LatihanHari Pertama

AturcaraSessi Pensyarah

Penerangan Kursus08:30-09:00 Firdaus

Ulangkaji Asas SCADA dan Kaedah Perantaraan SCADA09:00-10:30 Firdaus

Minum Pagi10:30-10:45

Rekabentuk RTU & Spesifikasi RTU (TNB)10:45-13:00 Firdaus

Makan Tengahari13:00-14:00

Foxboro C50 RTU14:00-15:00 Zuraini

Foxboro C50 RTU15:00-16:30 Zuraini

Tool & Test equipment16:30-17:00 Zuraini





Program LatihanHari Kedua


RTU – Xcell, PDSB, Talus,08:30-09:00 Azrai

RTU - RTU560, DF133109:00-10:30 Azrai


RTU Installation & RTU Test Plan10:45-13:00 Azrai


RTU Maintenance Policy14:00-15:00 Azrai

QUIZ FMEA15:00-16:30Azrai

RTU Document16:30-17:00Azrai





Program LatihanHari Ketiga


Substation Control System08:30-09:00 Osman






Substation Control System15:00-16:30

Osman


Osman





Program LatihanHari Keempat


Substation Control System08:30-09:00 Prem Raj







Prem Raj


Prem Raj





Program LatihanHari Kelima


Communication Overview08:30-09:00 Firdaus

Communication09:00-10:30 Firdaus


Wisp+ Protocol10:45-13:00 Firdaus


Competency Exam14:00-15:00

Discussion15:00-16:30

Q & A16:30-17:00





ASAS SCADA & KAEDAHPERANTARAAN

TELEKONROL





Session Overview• Very brief overview of SCADA

• Outstation = Substation• Different types of substation (from telecontrol point of view)

• Monitoring and Control

– Signal Types

– How they are derived

– Signal List• What

• Common

Operator's Workstation

Servers

Printer Operator's Workstation

Data RTU

RTU

RTU

CommunicationsSystem

Master Station OutstationCommunications

System





TYPES OF OUTSTATIONS

• Two Main Types:- – Substations Equipped with RTUs

• Typically referred to as Conventional Substations

– Substations Equipped with Substation Control

Systems

• Typically referred to as SCS substations

• Interfacing for both fundamentally the

same





Sistem Kawalan & Pemantauan

Pencawang Penghantaran

Isolator CT

VT

Transformer

OLTC

Battery

Charger

Circuit

BreakerBusbarEquipment Level

Tahap Perkakas

Bay Level

Tahap L itar

Stat ion Level

Tahap Pencawang

Netwo rk Level

Tahap Rang kaian

Bay Control Unit

(BCU)

Back-up ControlPanel

Protection

Relay Panel

Remote Tapchanger

Control Panel

Control

Panel

Remote

Terminal Unit

(RTU)

Supervisory

Interface

PanelGateway

Human Machine

Interface (HMI)

Station Level

Controller

Network Control Centre





PLANT

• What’s the plant? – Circuit breakers, relays, transformers etc

• What role does the Plant play?

– Source of Information – Target for control

SCADA I f i





SCADA Interfacing

Facilities

• Facilities such as SCADA Interfacepanels, transducers, interposing relays,

voltage-free contacts, cables etc provides

an interface between plant and the RTU





Kriteria Pemantauan & Kawalan

• Maklumat dan data yang diperolehi oleh

sistem SCADA perlu: - – Mencukupi (Suff icient/Adequate)

– Tepat (Accurate)

– Berdaya harap (Reliable)

– Cepat (Timely)

• Sistem SCADA mesti menghantar arahan

kawalan yang:-

– Selamat/Terjaga (Secure) – Berdaya harap/Boleh dipercayai (Reliable)

– Cepat (Timely)





Standard Signal List

• Under development• Proses

– 2 pasukan kerja – Primary equip (En. Rozemi)

Secondary (Dr Halim)

– Identify signals required – Trip, Urgent, Non-

urgent

– Prepare specifications to derive signals

• Review S/S Specs

• Prepare Telecontrol Signal List

• TTC/TWC approvals





Substations

• AIS, GIS• Voltage levels – 500&275kV, 132kV

• Circuit breaker types

– Operating Mechanism:- Hydraulic,Pneuematic, Spring

– Arc Quenching – SF6

• Circuit – tx bay, overhead line, etc





Information Flow

Master

Station Outstation

(RTU/SCS)

• indication & alarms• analog measured value• digital measured value• pulse counter value

SCADA Monitoring Direction





WHAT DO WE MONITOR?

• Status and Alarms• Sequence Of Events

• Counters/Pulse Accumulators

• Binary Coded Decimals• Analog Inputs





Status And Alarms

• Monitored by the RTU by using voltage-free contacts from the plant equipment.

– Voltage-free contacts from the circuit breaker

auxiliary contacts, for example, are used to

indicate the open or close status of the circuitbreaker.

– Voltage-free contacts from a protection relay

are used to indicate that the relay hasoperated. These inputs to the RTU are

referred to as Digital Inputs (DI).





Types Of Contacts

Types of Contacts :-

Form B - Normally close contact

Form C - Changeover contact

Form A - Normally open contact





Single Bit Indication

• For alarms such as protection relay operation, single-bit

indication is used.

• Single-bit indication uses the state of a single voltage-free

contact, typically the normally-open contact, to denote the

alarm state such as the operation of a protection relay.

• These voltage-free, normally open contacts will remain in theclosed or make state as long as the alarm condition persists.

• When the alarm condition is no longer present, the contacts

will return to the normal open state.

• Contacts from alarm annunciators that latch in the event of an

alarm and remains latched until a manual reset (typically by

an operator) cannot be used for SCADA monitoring purposes.





Single Bit Indications

Digital Inputs - Single Bit Indication

•Alarm - Overcurrent, E/Fault, etc

•Switches - Remote/Supervisory, Auto/Manual

0 or 1 = Open or Close

E.g.:-

ON 1OFF 0

0 1 0

OFF ON OFF

SI

Voltage Free Contacts





Double Bit Indications

• Status of Critical Devices

– To indicate the status of critical plant devices such as

circuit breakers and isolators, double-bit indication is

used.

– For double-bit indication, two contacts, typically Form

C contacts, are used to denote the state of the device.

– The double-bit indication is normally used for critical

plant parameters such that a fault in one of the

contacts will not result in a false interpretation of the

device status.

– All CB and isolator Open/Close status shall use

double-bit indication.





Double Bit Indication

Double bit Indication

C T0 0 = Travel

0 1 = Open

1 0 = Close

1 1 = Invalid

DI

Close 1

(52a) 0

Open 1

(52b) 0

00 0110 11

T

C

ClosedTravel

OpenInvalid






• Circuit Breaker Status – Double Bit Indication

CB Status

CB Auxiliary Contacts Double Bit

52a (no) 52b (nc) Bit 1 Bit 0

CB Travel Open Open 0 0

CB Open Open Make 0 1

CB Close Make Open 1 0

Invalid State Make Make 1 1






• Circuit Breaker Status – Double Bit Indication

The Protection & Control Code of Practice, 2nd Edition

(PTT/P/EP/-PCCOP02) requires that for voltage level of 275kV and

above, individual circuit breaker pole status shall be monitored. The

auxiliary voltage-free contacts of each individual circuit breaker

pole shall be individually wired to the SCADA Interface panel. Tomonitor the status of such circuit breakers, the RTU will be

connected to the contacts in series such that the failure of any pole

to open or close will result in an indication that the circuit breaker

has failed to open or close. The series connection of these contacts

will be carried out in the SCADA Interface panel.

• Monitor Trip for each Pole





Sequence of Events (SOE)

• Changes of state of devices and alarms can be

time-tagged by the RTU.• Time-tagged digital inputs referred to as SOE

points

• Allows the determination of the order ofoccurrence (sequence) of the events, – Allow the Operator to be able to distinguish the

sequence between events, i.e. which event happenedfirst, second, etc.

• Additionally, a time-tagged event also providesan indication of when they occur





Sequence of Events (SOE)

To enable the Operator to analyse the sequence of

events within the System, certain rules must beestablished and adhered to.

In TNB, the following SOE criteria have beenestablished:-•The Operator must be able to distinguish thesequence of two events if they occur at least 5milliseconds apart, if both events occur in the samesubstation

•The Operator must be able to distinguish thesequence of two separate events from two separatesubstations if they occur at least 10 millisecondsapart.





OUTSTATION – SOE

• Plant Interfacing Aspects for SOE inputs

– Derived from voltage free contacts

– SOE inputs must be taken directly from the contacts

of the initiating device and not derived from auxiliary

relays.

• To ensure accurate time tagging to allow the correct

discrimination of sequence,

• Inputs derived from auxiliary relays incur a delay that results

in inaccurate time tagging. (Relay pickup delay)

– Typically, the status of all primary switching devicessuch as CBs, isolators, and critical alarms are

assigned as SOE points.

Counters/Pulse





Counters/Pulse

Accumulators• Counter inputs are similar to digital inputs and are

derived from voltage-free plant contacts.• Counter inputs are typically used to count number of

circuit breaker operations or for energy (kWh) monitoringby counting pulses from an energy meter that is suitablyequipped.

• Counter inputs can either be from a single contact orfrom a pair of contacts.

• A counter input that is made up of two contacts is termedas Form C and requires that both contacts changes statefor the counter to be incremented by one. An example of

this application is using the CB Close auxiliary contactand the Master Trip relay contact to count the number oftimes the breaker trip on fault.

Counters/Pulse





Counters/Pulse

Accumulators

Types

Form A :-

Form B :-

Form C :-

Half cycle: 0 -> 1 & 1 -> 0Full cycle: only 0 -> 1

Half cycle: 1 -> 0 & 0 -> 1Full cycle: only 1 -> 0

Half cycle: 01 - 10 & 10 - 01

Full cycle: only 01 - 10





BCD Inputs

• Binary Coded Decimals – A combination of voltage-free contacts can be

grouped together to represent an integer value

expressed as Binary Coded Decimal format.

– BCDs are normally expressed as decades. – Four contacts form a digit which can represent 0 to 9.

– A two-digit BCD is also termed as a two decade input

and can represent from 0 to 99.

– The BCD input is most commonly used to representtransformer tap position.





BCD Inputs

BCD - Binary Coded Decimal input may be derived from anumber of consecutive digital indication

1

2

4

8

0

1

2

3

4

5

67

8

9

8 4 2 1 Decimal

0

1

0

1

0

1

01

0

1

0

0

1

1

0

0

1 1

0

0

0

0

0

0

1

1

11

0

0

0

0

0

0

0

0

00

1

1

1 digitBCD

0..9





Analogue Inputs

– As opposed to discrete values or states as in digital

inputs, analog inputs represent continuouslymeasured parameters or values. Examples are MW,

MVAr

– These parameters are typically measured using

transducers that are connected to the plant’s currenttransformers and voltage transformers.

– These transducers convert the plant inputs to a

scaled 4 to 20mA dc output which will in turn be fed

into the RTU. – RTU will convert the 4 to 20mA dc input into a scaled

digital value for transmission to the control center.





Analogue Inputs

TRANSDUCER

CT

VTRTU

Plant

Interface

4 TO 20 MA

0 TO 10 V

Plant equipment

Interface to transducer





Transducers

– Convert the primary values of the measured quantity

into electrical quantities which can be accepted by theRTU, i.e. scales the measured value down

– Allows standardisation of the input type into the RTU,

i.e different measurements eg MW, MVAr, Amps,

Voltage, Temperature etc, converts to one commonstandard electrical quantity eg. 4-20mA dc or 0-

10Vdc.

– Allows for some measure of isolation from the plant.

– Typically installed in control panels

Transducers General





Transducers – General

Configuration

Standards: IEC 688

+

-

TRANSDUCERS –

General Configuration

Transducer Auxilliary





Transducer Auxilliary

Supply

– Used to power the transducer – Must be dependable source

– TNB’s standard is from station dc supply • 110Vdc

• 30Vdc





Transducer Inputs

– Dependant on measured quantity, i.e. current

input for amperes, voltage input for voltagemeasurement etc

– Two types of input:-• Unidirectional – Eg. 0-15kV, 0-1000MW

• Bidirectional – Eg. -1000-0-1000MW

– Input range must cover full operating range• Eg: To measure 11kV voltage via 11000/110 VT,

the input range must be at least 130 Vac to

measure maximum of 13kV. If input range is110Vac only, transducer output will exceed rangeor over-range

MW MVAR Current





MW, MVAR, Current

Transducers

IR in IRout IB in IB outIR in IR out IB in IB out

MW-TDR MVAR-TDR

R B Y

+

-110 DC Supply

OUTPUT

4-12-20mA

VR VBVYVR VBVY

R Y

9

1

10

+

-5

MWOUTPUT 4-12-20mA

+ +

-

MW , Mvar & Current TRANDUCER WIRING

DIAGRAM

-

To RTU

MW

vdg

To RTU

MVar

o/p o/p

IY in IY out

Mvar

8

10 9

1

8

109

1

To RTU

Current

Current-TDR o/p

Output

4-20mA

+ -

110 DC Supply

C

+

-

CURRENT

VOLTAGE

B





Voltage Transducers

VOLTAGE

B

VR VB

o/p

i/p

+

-

110dc Supply

V

8

10 9

1

To RTU

Voltage

VOLTAGE TRANDUCER WIRING DIAGRAM

+

-

R Y





Transducer Output

– The measured quantity is converted to a

suitably scaled output – Output of transducer is input into the RTU’s

analog input module

– Types of outputs:-• Unidirectional Output eg 0-1mA, 0-20mA

• Reversible Output eg +/- 20mA

• Live Zero Output eg 4-20mA

– Output can be either voltage or current – TNB’s standard: 4-20mA DC.

• Facilitate detection of faulty transducers





Transducers

Transducer

Output

(mA)

Input

20

• Unidirectional Input

• Unidirectional Output

0 100%50%

50%

100%

Output





Transducers

Input

• Reversible Input

• UnidirectionalOutput

0 100%

100%

Output

-100%

50%





Transducers

Input

• Bidirectional Input

• Reversible Output

0

100%

100%

Output

-100%

50%

-50%

+50%

-50%

-100%





Transducers

Input


• Reversible Output

0

100%

100%

Output

50%

+50%

-100%





Offset (Live) Zero Transducer

Input

20


• Offset Zero or LiveZero Output

• Facilitates faultdetection

0 100%

4mA

20mA

OutputOffset (Live) Zero Transducer:

A transducer which gives a

predetermined output other than

zero when the measured quantity

is zero





Offset (Live) Zero Transducer

Input

• Reversible Input

• Offset Zero or Live Zero Output• Example: 4-12-20mA -600 –0 –600MW

0 100%

4mA

20mA

OutputOffset (Live) Zero

Transducer:

A transducer which

gives a predetermined

output other than zero

when the measuredquantity is zero

-100%

12mA





Suppressed Zero Transducer

Input


• Offset Zero or Live Zero Output

• Example: 0-4-20mA 0-231-320kV

• Increased resolution over the range thatmatters

0100%

4mA

20mA

OutputSuppressed Zero

Transducer:

A transducer whose

output is zero or a

constant given value

when the measuredquantity is less than a

certain value 70%





Dual Slope Transducer

Input


• Offset Zero or Live Zero Output• Example: 4-8-20mA 0-231-320kV


• Graph shows expanded end of scale

0100%

4mA

20mA

OutputDual Slope

Transducer:

A transducer with dual

resolution for two

measured quantity

rangesCan be expanded at

end of scale or

beginning of scale70%

8mA






Input


• Offset Zero or Live Zero Output• Example: 4-8-20mA 0-300-1000MW


• Graph shows expanded beginning of scale

0100%

4mA

20mA

Output


30%

16mA



T d A





Transducer Accuracy

• Example 1

– Meter has accuracy of +/- 1% fsd. Measuring

range is 100Amps. Therefore error is +/- 1

Amp. Therefore when the meter is reading 50

amps, the actual value can be between 49 to51 amps. Similarly when meter reads 5 amps,

the actual value is from 4 to 6 amps.

T d A





Transducer Accuracy

• Accuracy of readings

– Combination of the various measurementcomponents

– Overall accuracy:-

• Source Accuracy eg accuracy of CTs, VTs.

Typically Class 1, i.e. 1%• Accuracy of the transducer (typically Class 0.5 or

0.2)

• Accuracy of the analog input module in the RTU(0.1%)

• Accuracy of conversion at the Control Center

– Accuracy always quoted with temperature reference,i.e. calibrated at. Typically 20°C. TNB = 32°C.

S li & C i





Scaling & Conversion• Plant -> Transducer-> RTU -> Master Station

• Plant: CTs and VTs convert primary to secondary, eg:- – 800/5 CT converts 800A to 5A

– 11000/110 VT converts 11kV to 110Vac

• Transducer converts the secondary values into astandard value, i.e DC milliamps

• RTU converts the output of transducer into a digitizedvalue – Value depends on the A/D converter chip,i.e. number of bits the

A/D chip converts the analog value to.

– Digital value referred to as Counts

• To get Scaling, must find out what engineering valuescorresponds to 0 counts and the maximum counts. Insome systems expressed as a factor, in othersexpressed as two sets of points

A/D C i





A/D Conversion

• Some Basics First – Bits and Bytes

– If you have n number of bits, you can count from 0 to2n-1. Eg. With 3 bits, you can count from 0 to 7.

• An Analog to Digital Converter (ADC) is aintegrated processor (chip) that converts ananalog input to a digital value or representationof that value.

• TNB’s RTU Specifications requires the ADC tohave a minimum of 12 bits plus sign, i.e.converts from -4096 to +4095, -214 to +214-1

20 21 22 23 2n-2 2n-1

Bit 2 Bit 1 Bit 3 Bit 4 Bit n-1 Bit n

S B i





Some Basics

A REMINDER:For a star-connected system,

line voltage = 1.73 X phase voltageline current = phase current

For mesh-connected system with balanced load,line voltage = phase voltageline current = 1.73 X phase current

For star- or mesh-connected system with balanced load,

Total power = 1.73 X line current X line voltage X power factor

(W= 3 V A Cos Ø)





Scaling & Conversion

Example 1: Current Transducer

CTR 400/5

Current Transducer

i/p: 0-5A

o/p: 4-20mA dc

RTU12 bit plus sign

-4096 to 4095 reversible input

0-4095 unidirectional input

A

BCD

Plant

(A)

Transducer

Input (B)

Transducer

Output (C)

RTU

Counts (D)

0A 0A 4mA 0

200A 2.5A 12mA 2047

400A 5A 20mA 4095

Raw

Count

0 4095

Eng

Scale

0 400A

Scaling factor = 400 Amps

4095 Counts

= 0.09765625 A/count





Scaling & Conversion

Example 2: Power TransducerCTR 1600/1

VTR 132000/110

MW Transducer

i/p: 0-1A, 0-126V

o/p: 4-20mA dc

RTU12 bit plus sign

-4096 to 4095 reversible input

0-4095 unidirectional input

A

BCD

Plant Xdcer i/p Xdcr

Output

RTU

Counts Amps Volt Cos Ø MW Amp Volt

0A 0kV 0 0 0 0 4 mA 0

1600A 132kV 1 365.81 1 110 17.97mA 3576

1600A 151.2kV 1 419.02 1 126 20 mA 4095

Maximum Power Range = 3 x VTR x Max Volt Input x CTR x Max Current Input x Max Cos Ø= 1.73 x 132000 x 126 x 1600 x 1 x 1 (Cos Ø = 1)

110 1





Command Flow

Master

Station

Outstation

(RTU/SCS)

SCADA Control Direction

Output Commands

•CB Trip/Close Control

•Analog Setpoint Control

•Digital Setpoint Control

S i C t l





Supervisory Control

The Protection & Control Code of Practice

specifies that, from the Network Level (ControlCenter), it shall be possible to:- – Control all switchgears with the exception of earthing

switches. This includes circuit breakers and isolators.

– Set reference values for• Automatic Voltage Controller (AVC)

• Generator Controller MW set-point

• Static VAR Compensator (SVC)

• Capacitor and reactor controller

– Raise and Lower tap changer position

– Override the AVC when the tapchanger is inautomatic mode

– Reset lockout relays

S i C t l





Supervisory Control

• All supervisory control actions are enabled onlywhen the Supervisory/Remote switch for thedevice is in the Supervisory position anddisabled when it is in the Remote position.

• S/R switch is required for safety purpose; toprevent Control Center from operating thedevice when there is work at site

• The supervisory control scheme shall adhere tothe interlocking system for safe operation of thedevice.

Control Proced res





Control Procedures

• 132kV CBs

– Caters for synchronizing-LLLB,DLLB,LLDB,DLDB

– Control sends close command and control scheme

takes care of all checks

• RTCP – NLDC sends Override Select command which will

defeat AVR (AUTO), Indication brought back as

Supervisory Override ON

– NLDC sends Raise or Lower – NLDC sends Override Cancel command

– Parallel scheme only Master can be controlled

S per isor Control





Supervisory Control

There are two basic ways Supervisory Control can

be accomplished:- – By initiating a contact closure

• (Digital Output) – Double Point Control -Trip/Close ***

– Single Point Control – Raise/Lower (Pulse Duration)

– Jog Point (Number of Pulses) – Operator Control

– Pulse Train – Program control

– Digital Setpoint – binary pattern

– By sending an analogue value• (Analog Output)

Supervisory Control – Digital





p y g

OutputSupervisory control of circuit breakers, switches and

equipment that have discrete states such as ON, OFF,OPEN, CLOSED, etc, is achieved by contact closure.

Control Center sends a command to the RTU,

RTU energizes an intermediate relay, referred to as

the Heavy Duty Interposing Relay (HDIR).

The contacts of the HDIR then make to complete the

control circuit of the plant equipment.

Heavy Duty Interposing





y y p g

Relays (HDIRs)• HDIRs increases the RTU’s control output

switching capacity• Provides some isolation between RTU and plant

• Cretes a link between between differing voltagelevels – Eg RTU 48Vdc, Plant 110Vdc

• HDIRs typically installed in SCADA InterfacePanels

• In TNB, there are 110Vdc HDIRs as well as48Vdc HDIRs

• There are two ways which HDIRs can be wired

HDIR Energization – Free





g

Contact

To Plant

Control

Circuit

To RTU

Substation DC Supply(110Vdc or 30Vdc)

HDIR

• RTU provides

voltage free contact

• HDIR gets coil

voltage from station

dc supply

HDIR Energization Direct





HDIR Energization – Direct

48 VDC (+)

0VDC HDIR

To Plant

PlantRTU

• RTU provides +ve and –ve supply directly to

energise the HDIR coil

HDIR Wiring





HDIR Wiring

• TNB’s RTU Specs specify that RTU must be

able to support all three control configurations

– Voltage Free Contact

– Directly supply 48Vdc to energize HDIR

– Directly supply 110Vdc to energize HDIR• Telecontrol recommending that plant be wired

up to accept voltage free contacts from RTU and

to use station DC to energize HDIR

– Not too much of an issue as RTU will be part

of new S/S

Specifiying HDIRs





Specifiying HDIRs

• Electromechanical relays consist of a coil that

causes a mechanical movement of a contact set.• Coil

– AC or DC

– Coil’s input range, nominally +/-20% of rated voltage

– Switch on voltage

– Holding voltage (switch off)

– Holding voltage lower than switch on voltage

– Nominal current – current that coil typically draws

when operated• Current consumption high for coils with low resistance

• Current consumption low for coils with high resistance

HDIR Contacts





HDIR Contacts

Normally Open (NO) or Form A Contact:

A relay contact that is open when not

energized

Normally Closed (NC) or Form B Contact: A relay contact that is closed when not

energized

Both NO and NC or Form C Contact:

A contact set that has both normally open

and normally closed contacts, and acommon termination for power. State of

both contacts change when relay is

energized

HDIR Contacts



Jabatan Kejuruteraan (Telekontrol) -Dec 2005Bahagian Penghantaran Firdaus Yon Institut Latihan Sultan Ahmad Shah(ILSAS)

HDIR Contacts

Single Pole, Single Throw(SPST)

Double Pole, Single Throw

(DPST)

Single Pole, Double Throw

(SPDT)

Double Pole, Double Throw

(DPDT)

HDIR Contacts




HDIR Contacts

• Important to determine correct rating

• Must first determine function of relay:-

– DC or AC switching?

• Harder to switch DC loads because there is no zero current

point as in AC, therefore difficult to quench the arc. Also as

direction of current is fixed, contacts suffer from contact shift.

– Type of Load?

• Switching capacity in relay specs relate to resistive load.

• For inductive circuit, high counter emf is generated

HDIR Contacts




HDIR Contacts

• Inrush Current – Depends

on type of load

Type of Load In-rush Current

Resistive Load Steady State current

Solenoid Load 10 to 20 times the steady state currentMotor Load 5 to 10 times the steady state current

Incandescent Lamp

Load

10 to 15 times the steady state current

Capacitive Load 20 to 40 times the steady state current

Transformer Load 5 to 15 times the steady state current

HDIRs




HDIRs

– Typically installed in control panels

– Minimize use of long wires in relay contact

circuit as inrush current may become a

problem due to stray capacitance existing

between the wires

HDIRs Inductive Load




Switching – Types of inductive loads:-

• Relay sequence circuits, DC Motors, DC solenoids

– When inductive loads are switched off, acounter emf of several hundred to severalthousand volts develop across contacts ->

damage contacts and reduces life – If current is small (<1A) counter emf will cause

glow or arc discharge. Causes black deposits(oxide and carbides) on contacts. Result in

contact failure. – Important to absorb surges – use diodes etc,

contact protection circuits

Supervisory Control - Analog




OutputSupervisory control of devices that allows regulation such

as automatic voltage regulators, setpoint controllers etcthat can accept an analog value as a control or

regulating input uses Analog Output control.

Control Center sends a digital representation of an

analog regulating value to the RTU,RTU converts the digital value it received from the

master station and generates an analog output value

and send to the target device

The target device, such as an AVR or a setpointcontroller takes this value and uses the value to effect

a control action

SCADA Interface Panel




SCADA Interface Panel

• Also referred to as LDC Interface Panel or

Supervisory marshalling cubicle.

• Acts as a central cabling and termination point

between RTU and plant

• SCADA termination points from each plant panelis cabled to and terminated at the LDC I/F Panel.

• Isolating terminal blocks allow isolation between

plant and RTU




RTU Cabling System

RTU

CircuitBreakers

Comm

Box

AC

Panel

DC

Source

LDC

I/FPanel

ControlPanels

RelayPanels

RTCCP

Plant

Summary



Summary

• Digital Inputs

– DB, SB, SOE, Counters, BCDs – Interfacing

• Analog inputs – A/D

– Transducers

• Supervisory Control – Digital Outputs

• HDIRS

– Analog Output

• Cabling System

RTU training ILSAS1

Documents

Transcript of RTU training ILSAS1