Bus Bar Protection REV 1
Transcript of Bus Bar Protection REV 1
-
7/28/2019 Bus Bar Protection REV 1
1/18
BUS BAR PROTECTION AND
LBB PROTECTION.
By
Y. k. Pandharipande.
-
7/28/2019 Bus Bar Protection REV 1
2/18
BUS BAR PROTECTION AND LBBPROTECTION
PERFORMANCEREQUIREMENTS
Stability
High Speed Operation
Selectivity
Reliability
Sensitivity
Suitable for Use with moderate CT Ratings.
Extendable to changes in Bus Bar configuration & additionof Circuits.
-
7/28/2019 Bus Bar Protection REV 1
3/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTIONCIRCULATING CURRENT DIFFERENTIAL PRINCIPLE
CURRENT DISTRIBUTION EXTERNAL FAULT
CURRENT DISTRIBUTION INTERNAL FAULT
-
7/28/2019 Bus Bar Protection REV 1
4/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PRIOTECTION
A. HIGH IMPEDANCETYPE
Relay Branch made High Impedance to limit differential currentdue to unequal CT saturation on external fault.
Requires exclusive CT core of identical ratio and rating.
Simple in design and execution.
-
7/28/2019 Bus Bar Protection REV 1
5/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION
B. LOW IMPEDANCE (BIASED) TYPE
Through current Bias increases differential pick-up on externalfault to ensure stability.
Tolerant to CT mismatch and can use shared core. Comparatively more complex in design and execution. Practical schemes provide CT saturation detectors to enhance
stability.
-
7/28/2019 Bus Bar Protection REV 1
6/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION (87)HIGH IMPEDANCE SCHEME
If B CT fully saturates on external fault,Vs = If/n (Rct + 2Rl) Volts.
Relay Branch Impedance = Vs/Is, where Is = Setting current of Relay.
External Stabilising Resistor RST = Vs/Is VA /Is, where VA = RelayVA burden at setting current.
-
7/28/2019 Bus Bar Protection REV 1
7/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION (87)HIGH IMPEDANCE SCHEME- Typical Setting Workout.
Max. Through fault Current (If) = 20,000A (Prim) / 20A(SEC)
Vs = 20 (5 + 1) = 120V
Stabilising Resistor (RST) = 120/0.2 1.0/0.2 = 600 - 25 = 575 ,(assuming relay VA burden = 1 VA)
-
7/28/2019 Bus Bar Protection REV 1
8/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION
HIGH IMPEDANCE SCHEME Typical Setting Workout.
Primary Fault Current setting (assuming number of circuitsconnected to Bus Bar, N=10)
= CT Ratio (Is + N. Im)
= 1000 (0.20 + 10 x 0.03) = 500A.
-
7/28/2019 Bus Bar Protection REV 1
9/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION (87)HIGH IMPEDANCE SCHEME Need For Metrosils.
Peak Voltage across CT Secondary for Max. Internal Fault= 2 2 [Vk x (Vp Vk)]
Vk = 240V, Vp = 20 (575 + 25) = 12000V
Peak Voltage = 22 [(240 x (12000-240)] = 5300V
-
7/28/2019 Bus Bar Protection REV 1
10/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION
HIGH IMPEDANCE SCHEME Need For Metrosils.
If Peak voltage exceeds 3000V threatening secondary
insulation, Metrosils (Non-linear resistors) are used to limitvoltage to safe value (within 1000V) on internal fault.
Metrosil offers high resistance at lower voltage levelswhich drastically reduces at higher voltages, therebyquenching the voltage across relay branch.
Typical Metrosil EquationV = C x I ( C = 900 , = 0.25)
-
7/28/2019 Bus Bar Protection REV 1
11/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION
HIGH IMPEDANCE SCHEME -CT SUPERVISION (95)
Required to detect CT open circuit on load to prevent maloperation. Connected for alarm & short CT bus wires on operation. Time delayed to avoid operation on internal / external faults (3Sec) Voltage relay with sensitive setting (2 -14V) is used. Normally set to detect primary unbalance of 25A or 10% of least loadedcircuit. Also should not operate with normal unbalance on load.
-
7/28/2019 Bus Bar Protection REV 1
12/18
BUS BAR PROTECTION AND LBBPROTECTION
BUS BAR PROTECTION CT SWITCHING.
-
7/28/2019 Bus Bar Protection REV 1
13/18
BUS BAR PROTECTION AND LBBPROTECTION
TYPICAL 2 ZONE SCHEME WITH INDEPENDANT CHECK
-
7/28/2019 Bus Bar Protection REV 1
14/18
BUS BAR PROTECTION AND LBBPROTECTION
TYPICAL 2 ZONE SCHEME WITH INDEPENDANT CHECK
D.C. CIRCUITS.
20K resistor on negative side used for cathodic protection.
-
7/28/2019 Bus Bar Protection REV 1
15/18
BUS BAR PROTECTION AND LBBPROTECTION
LOCAL BREAKER BACKUP (LBB) PROTECTION
NEED
Provides local isolation when breaker gets stuck onfault.
Ensures comparatively faster clearance than remotebackup.
Avoids wide spread interruption and enables fastrestoration.
-
7/28/2019 Bus Bar Protection REV 1
16/18
BUS BAR PROTECTION AND LBBPROTECTION
LBB PROTECTION OPRATING PRINCIPLE & CT CKTS.
-
7/28/2019 Bus Bar Protection REV 1
17/18
BUS BAR PROTECTION AND LBBPROTECTION
LBB PROTECTIOND.C. CKTS USING BUS BAR PROTECTION TRIP LOGIC.
LBB CURRENT CHECK RELAY (50)Current Setting Range 20-320% or 5 -80%In (Recommended setting - 5%
for Generator & 20% for Other Circuits)
LBB TIMER (2/50) Range o.11.0 S (Recommended 0.20S)
-
7/28/2019 Bus Bar Protection REV 1
18/18
BUS BAR PROTECTION AND LBBPROTECTION
LBB PROTECTION TIMER SETTING CRIETERIA
TLBB = TCB + TDO + TM TPU,
Where TCB = C.B. Trip Time, TDO= Current Check relay DO time,TM = Safety margin, TPU = Current Check relay PU Time
Normally,200ms delay recommended which is faster thanremote backup and allows sufficient time for normal C.B.
tripping.