Engineering Control Drawing

8/18/2019 Engineering Control Drawing

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Engineering Control Drawing

Qazi Arsalan Hamid

Testing and Commissioning Engineer


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Thanks to my Mother and Father who always

encourage me to learn new things and spread it

without expecting reward

Also thanks My Friends Mr. Khalid Anwar and Mr.

Rizwan Syed ,they helped me understanding

Different Concepts regarding Engineering.


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Engineering Drawing

Drawing is like X Ray for engineers of power grid. Engineer can examine the three different aspect or

classes of grid equipments , whenever we are working in power grid or any master substation we need

to concentrate on

Equipment which need to be protected

Equipment which need to be sensed abnormal/normal Condition

Equipment need to be take action in case of normal/abnormal condition

basically in every substation there are

Sensing panel(Relays)

Control Panels

Action Panels(Circuit breakers,contactors etc)

Auxiliary Circuits (latching relays, timing relays, Sockets etc)

these all are interconnected , and modern relays make it easy for Grid peoples as it provide multi

function in one package.

interconnection of relays and panels is done by about 6sqmm low voltage insulated wires as modern

relays are low voltage operated with very low burden.

i am taking one example for capacitor panel protection engineering drawing , and we will try to

understand it what that drawing informing us.

in all drawings , they 1st give you contents of drawing then legends , but remember some legends must

be on engineer finger tips , K sysmbol is universally accepted for auxiliary relays, remember auxiliary

relays are relays used for circuit isolation, multiple contacts and indication purposes . Q symbol is forBreaker , Relays will be shown by there ANSII numbers like

51 for OC

51N for Earth Fault overcurrent Relay

64G for ground Detector relay

74 for trip circuit supervision relay


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86 for master trip or lock out relay

96 for DC supply supervision

87 for differential relay

21 for Distance Relay

27 for undervoltage relay

59 for overcoltage relay

81 for frequency relay

Breaker failure relay is intertripping relay , but it will show by associated breaker

but nowadays in some drawing you see relay make and number in place of ansi code, like RET670,

7SJ512 ,P121 etc

Most of the drawings are showing relays in inactive forms , but remember when relay shown in drawing

is active it must be mention in drawings.

in drawing, first page is dedicated to front view of panel where relays, indication LEDs, and control

equipmentof relays and panels are shown

then main circuit protection layout is given , in which source of power, conductor , load with protection

devices are shown. but for direct purposes the protection detailed lay outs are mention in many drawing

, if you are designated for particular section drawing you need to concentrate on that section only no

need to tele complete grid drawing, but it is necessary to give keen and thoroughly look on assigned

section drawings.


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here you can see the protection circuit, which is linked with 13.8KV busbar, here one Potential

Transformer is connected line to ground for protection purposes. whenever PT is connected line to line

then line to line voltage would be the PT output voltage, but when VT connected between line to ground

the out put voltage would be nominated voltage/sqrt(3)

here nominal voltage is 120V , so pt output would be 120/sqrt(3)=69.282V

here line need to be protected is 13.8Kv so voltage ratio would be like

13.8KV/sqrt(3):120V/sqrt(3):120v/sqrt(3)

here i mention two output because my VT is multicore , each core with dual class of metering and

protection , this is advancement in technology .

VT metering classes are 0.1,0.2,0.5,1 and 3 and protection classes are 3p and 6p , here i adopted 0.2 for

metering and 3p for protection purpose. burdens are 25VA in both cases of metering and protection.

We protected Out pt by fuses (HRC) from Primary side and Miniature circuit Breakers(MCBs) from

secondary side as per recommended practices.

we have multifunction relays SEL-487V and C-70 here for under/over Voltage (27/59),

instantaneous/Inverse Over Current relay(50/51), instantaneous/Inverse Over Current earth fault

relay(50/51N), non directional Overcurrent relay(59ND),Directional Overcurrent Relay(67), Inter tripping

or circuit breaker failure relay(CBF), Trip circuit supervision Relay(TCS) , negative sequence overcurrent

relay (46). in C-70 you have thermal overload protection function also 49.


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now see there are five test sockets , all sockets are used for capacitor bank protection check . these

sockets must be wired properly , also one thing which must be kept in during testing is that never

remove test socket cover while system is alive , it is not recommended.

another micom relay is installed P139, metering arrangement is shown also PM and DPDM.

TS2 have PT connection and SEL 487 connection

TS1 have CT connection and SEL 487V connection

TS3 have metering connection, CT connection amd C-70 Relay connection

TS4 have PT connection and C-70 relay connection.

TS6 have P139 relay connection

Test Socket is used for testing and metering purpose of Protection and metering equipment , always use

when circuit is dead, live line testing is not recommended. with help of test sockets we can test ourrelays and other equipments with disturbing the equipment wirings.

here we have one multi core and multi ratio current transformer, the difference in it is simple ,in multi

core you can utilize all core for the protection,metering and control purpose , unused ct cores must be

short. in muti ratio CT you can use only one particular or reuired ratio at a time i.e if you have

800:400/1A , then either you used this CT as 400/1 or 800/1, not both at a time . this multi coring or

multi ratio thing is done by tappings at CT secondary cores.

in multi ratio CTs , the secondary sides are already short so no need to short used CT secondary, but in

multi core CTs unused CTs must be short because in multi core CT each Core represent separate

unshorted CT.

now we are moving to next drawing pages.

i have in my drawings the AC circuit Protection Logic Drawing


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here you can see our 13.8 Kv circuit breaker is coupled with two breakers and one reactor, reactor is

current limiting device and harmonic suppressor. neutral balance CT is low rated CT with 10/5A rating,

the current in neutral while capacitor bank is healthy will be ZERO, but during unbalancing some current

flow in this CT and relay associated with this CT signalled breaker to get trip. in this case class of CT is 5pwith ALF of 20 , means this CT will have errors less then 5% upto 200A in primary neutral circuit which

will be accidental but not usual.

we now moving forward , now we have DC logic Drawing , remember we always kept DC in back up in

any substation , and also run our most controlling and protection euipment via DC so when in case of

power failure we can get stored DC supply for protection and control panel.


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here you can see the SEL 487V relays is supplied from DC supply 1 , BCPU,trip coil 1 via tripping relay 94,BCPU via tripping relay 94,HMI /SAS signalling via tripping relay 94 and DC supply 1 via tripping relay

94,close block with lock out relay 86, Trip coil -1 with lock out relay 86 ,BCPU with lock out relay 86,

HMI/SAS signalling with lock out relay 86, DC supply with lock out relay 86,


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now in next drawing page we will review the panel illumination and Heater circuit.

both heater and lightning panel is supplied via 220V ac Supply, we provide thermal MCBs, these MCBs

will trip when thermal affect increase due to over current, or itself current raise above the current

setting of MCB.

in socket circuit we provide 1 fluorescent light with sockets. across contact 1,2 and 3,4 and 13,14

selector switch is given , when selector switch is at 1,2 your heater is at auto position humidistat(HMT)

will sense heat insight cubicle and will auto off heater when set limit cross. at 3,4 heater can be

manually off and on , at 13,14 you can test healthiness of your heater circuit.


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in next page we are observing the DC supply Distribution circuit ,

both main protection circuit Main-1 and Main-2 power will be supplied from 125V dc supply, both

supply is equipped with MCBs. this shows that our protection panel is DC powered so in case of grid ACsupply failure or fault in Grid the relays will remain effective.


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in next drawing , we will review CT circuit

in this the CT is wired 1st in Test block , then from test block it is wired to the relay , here you can CT is

Star connected , see contact 3S1 contact of R,Y and B phase CTs are connect with each other to form

Earth (return path) .


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then we have metering CTs connection , again via Test block , so you can check any time the Meter

accuracy and Metering CTs characteristics , remember that safety factor it is the margin by which your

metering CT is safe , here it is 5 which means up to 5 times of current the metering CT will be safe to

operate , for knowledge please remember that saturation point of metering is always less than the

protection CTs.

below metering CTs, we have Protection CTs for Main-2 protection circuit via Test block. when CT is not

in used for protection or metering it must be short circuit by wire or metallic jumpers , nowadays many

test block are equipped with inside short jumpers , means if you remove test block cover the CT side

should be shorted automatically.

but here if you want to short your CT following operation required

Metering CT

2,5,8 and 10 must be open and 1,4,7,9,and 14 must be closed

Protection CT

10,12,14 and 16 will be open 11,13,15 and 18 must be closed. so CT will be short with system earthing.


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in next drawing we are observing the Neutral unbalance CT and PT circuit.

one neutral unbalance CT via Test block is connected to C-70 relay , in C-70 relay there is function

named as 46UB, which is unbalanced detection relay due to negative sequence current.

basically these relays equipped with two stage of tripping , 1st one is activate when value increase upto

110% of nominal voltage , in second stage it will activate when value get exceed from 110 % of nomianl

value.

also one PT connection to Main-1 protection is shown here.


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in next drawing we have two PT connection drawing for Main-1 and Main-2 Protection circuit.

these are PTs circuit of 13.8 KV switchgear, both PTs are 3p class protection PTs.


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in this we will review Relays connection with Test Blocks

from this drawing you can easily Test relays by just removing cover of block and injecting current. here

TS1 test block is from Current Transformer connection and TS2 block for VT connection (phase and

unbalance compensation VTs)


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in next drawing we are going to examine the Main -1 Cap Protection Binary input module

from left you see different relaying condition , after which 86(lock out relay) and 94(tripping relay of

breaker) activated. lock out relay will prevent breaker to get on until lock out relay electrically or by

hand reset .

tripping relay is auxiliary relay of breaker which mount within circuit breaker assembly.


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now let see trip/lock out relay circuit.

when in case of fault , the tripping relay 94 activated and same time lock out relay 86 operated , and

break switch 27 will close and Reset Switch (make switch) will be at apart(off) position , the lock out

relay can be reset electrically or manually , wiring shows that manual connection is bypassing the

electrical reset circuit. when we reset electrically or manually the 25 make switch will be make but

sensing from 27 will remain intact , if fault still in circuit the relay will not reset and circuit remain off.

also not 27 and 25 are coupled ,one will on at a time.

here we provide DC supply provision relay which detect low voltage or absence of voltage in this control

circuit. but this DC supply provision only alarm or indicate the low voltage or absence of voltage as there

is no breaker trip provision is provided in it.


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hope that document will provide some help in understanding Electrical control drawings.

thank you for reading this material.

in case of any flaw or mistake please inform me so i can correct it.

Regards,

Engr. Qazi Arsalan Hamid

Testing and Commissioning Engineer

[email protected]

Documents

Engineering Control Drawing