Surge protection with shah jaydeep

JAYDEEP SHAH (E.C ENGINEER) radhey04ec@gmail.com
2/17/2018 SURGE
PROTECTION.
JAYDEEP SHAH (E.C)
AHMEDABAD - INDIA

DOCUMENTATION INCLUDE:
 GDT GAS DISCHARGE TUBE
 6KV SURGE PROTECTION SCHEME
 MOV AND GDT COMBINATAION
 MOV BASIC
 MOV SELECTION WITH EXAMPLE
 FUSE RATING FUSE SELECTION

For outdoor applications, the standard calls for a recommended surge protection
level of 6 kV/3 kA for low exposure conditions and, 10 kV/10 kA for high
exposure conditions.
 Choosing the correct suppression device:
The LED driver without external protection TVSS (transient voltage surge
suppression) is designed to handle surges in the 2-3 kV range for the 1.2/50usec
combi-pulse (2 ohm). To achieve a system protection level of 10 kV/10 kA, the
external TVSS device must be able to limit the voltage that appears at the driver
terminals (L, N, G).
To protect for a 10 kV, 1ohm surge (10 kA), the required clamping voltage of the
external MOV (or other TVSS) needs to be lower than 1 kV at 8 kA.
(10 kV-2 kV)/1ohm=8 kA.
 Here is what to look for in the MOV ratings:
1. AC voltage rating: This needs to be sufficiently higher than the normal operating
voltage range. 325 Vac rating is recommended.
2. Maximum surge rating: The10 kA rating is required for the high exposure level.
20 mm diameter MOVs can typically be found with this rating.

How to connect the MOVs in the fixture:
1. Connect 1 MOV between Line and Gnd
2. Connect 1 MOV between Neutral and Gnd
3. Connect 2 MOVs in parallel between Line and Neutral. Connecting 2 MOVs in
parallel between Line and Neutral
V1 : Between L – N
V2 &V4 : Parallel connection & Common GND
V3 : L – GND
Why not design a LED driver to survive 10 kV directly without clamping to earth
ground?
In a typical LED system, the LEDs are mounted to a heat sink which is connected
to earth ground. A common mode surge voltage of 10 kV would break over the
insulation between the LEDs and the heat sink in most installations and, therefore,
voltage clamping is required. The typical breakdown of the LEDs to the heat sink
is in the order of 2 kV, so clamping below this level is necessary even if the driver
is designed to handle the higher voltages. This is why a driver design that can
handle 10 kV surges does not help the system pass 10 kV. The voltages must be
clamped to a level that the LED-to-heat sink insulation can safely withstand to

prevent LED failure. Also, not clamping the common mode surges would put a
large burden on the wiring inside the fixture as everything would need to be
designed to withstand 10 kV (wires, connectors, wire nuts, etc.). Implementing the
above suppression circuit in the fixture eliminates the need to the high withstand
voltages on the wires, connectors, and LED-to-heat sink interface.
 GDT : GAS DISCHARGE TUBE
GDT : Special type of gas filled tube for providing protection against lightning and
power surge.
Tube have two electrode inside gas filled close envelope.
Electrical characteristics of this tube depends upon pressure and composition of
gas. There will be conduction inside GDT due to ionization of gas molecules.
Its responds time very fast less than 100 ns.
It is switching type lightning surge protection components which is use as parallel
in with L-N or L-G in circuit.
It has no polarity and easy to install.
It is used in protecting high frequency communication line but not used in AC
circuit directly.
It must be added clamping type protecting component in AC.

GDT used widely for protecting consumer electronics circuits.
Why use?

Once the gas is ionized, breakdown occurs and the gas tube changes from a high
impedance state to a virtual short circuit and thus, any transient will be diverted
from and will not reach the protected circuit. The arc voltage (the voltage across
the gas tube while the gas tube is conducting) will typically be 15 volts. After the
transient has passed, the GDT will extinguish and again appear as an open circuit.
USEFULL TERMS:
DC SPARK OVER VOLTAGE: Defined as DC break down voltage tested at
100 V/S or 1000 V/s rise.
Impulse spark over voltage: It is impulse break down voltage tested at 100 V/uS
or 1000 V/uS.
Nominal Impulse Discharge current: It is lightning impulse discharge current
which GDT can with stand at 8/20 uS waveform.
{ 8 /20 uSec waveform = 8 uS rise time & 20 uS 50% decay time }
AC Discharge current : It is defined as with stand AC power frequency current
ability at 50 Hz.
Additional Information:
 MOVs can be placed in series with GDTs
 MOV will help cut off the follow current and allow GDT to turn off
 During surge event, MOV will clamp and conduct first into a low impedance
state; then GDT will break-over and create the arc.
 When surge subsides, the MOV will go back to high impedance state and will
quench the follow current and allow GDT arc to be extinguished
Littlefuse ACxxx GDT series design for power line.
Here is one example circuit :
Input Voltage = A.C – 230 V
V1 /V2 = ERZV14D911 OR TMOV20RP575E LITTLE FUSE.
G1 = LITTLEFUSE AC 240 SERIES.

EX:
Littelfuse AC series two-electrode line protectors provide a high degree of surge
protection in AC line applications. The two models, AC120 and AC240 are
designed for use with 120VAC and 240VAC lines respectively. They are able to
extinguish AC follow-on currents of at least 200A.
VARISTOR MOV SELECTION

Background:
– MOV (Metal Oxide Varistors) can degrade over lifetime due to surge events
– MOV material can weaken due to multiple surges and develop “memory” path
– MOV at end-of-life will start to leak current with nominal system voltage
applied
 Problem:
– Leakage will heat up the MOV and impedance will continue to drop leading to
thermal run-away failure
 Solution:
– Select TMOV series products to control MOV end-of-life (EOL) conditions.
– TMOV™ MOVs have integrated thermal protector built inside the disc which
will open upon thermal heating of MOV.
– Use of TMOV will prevent catastrophic failure of MOV disc during EOL
condition
EX:
FOR AC INPUT RANGE 180 – 325 VAC
For suppress switching spike and surge just used varistor across L & N
ERZV14D751 OR ANY (750V Varistor voltage, MAX AC RMS = 460, MAX
DC = 615V ,IP = 50 A series varistor for best performance to suppress switching
spikes.)
OR use TMOV TMOV20RP550E .

 FUSE RATING SELECTION :
FUSE RATING = MAX IN CURRENT × 125 %
FOR EXAMPLE : MAX INPUT CURRENT = 1 AMP.
FUSE RATING => 1.25A
WE CAN USE 1.40 AMP FUSE FOR PROTECCTION PURPOSE.
A fuse rating is the current need to blow (break) the fuse. When a fuse has blown
it removes electrical power from an electrical circuit. The fuse rating is usually on
the side of the fuse. The fuse rating is usually defined in 'amps' – amps are the unit
of measurement of electrical current.
Power (Watts) = Current (Amps) x Voltage (Volts)
Therefore:
Current = Power/Voltage
Therefore:

Fuse rating = (Power/Voltage) x 125%
OR, put another way:
Fuse rating = (Power/Voltage) x 1.25
OR, put another way:
Fuse rating = (watts/volts) x 1.25
 Note the power of the appliance – usually in the appliance manual,
 Note the voltage (240 volts in the INDIA).
 Use the next highest fuse rating after the calculation.
o Say the calculated fuse rating is 2.2679 amps, use a 3 amp fuse.
 MOV SELECTION EXAMPLES :
Circuit conditions and requirements:
-120VAC circuit
- Current waveform for surge is 8x20s; voltage is 1.2x50µs
- Peak current during the surge is 3,000A
- Requirement is to survive 40 surges
- Other components (transformer, capacitors, etc.) are rated to withstand 1,000V
maximum.

Approach to finding a solution: - To find the voltage rating of the MOV, allow for
20% head room to take into account voltage swells.
• 120VAC x 1.2 = 144VAC
• So look at 150VAC rated MOVs
• Determine which MOV disc size to use – identify those that minimally meet the
3,000A surge requirement
-Use Pulse Rating Curves to determine pulse capabilities of each series per the 40
pulses @ 3,000A requirement
- Use V-I Curve of selected MOV to verify that the peak voltage will be below the
1,000V ceiling.
Data sheet review – Peak Current rating
• From the problem statement, need > 3,000A capability for 150VAC disc • Per the
table, the 14mm disc can pass at least one 3,000A surge pulse

Pulse Rating Curves for 14mm LA series
• Locate pulse width (20μs) on the x-axis
• Find where vertical line intercepts 3,000A point
• In this case, we find that the LA MOV can survive 1 to 2 pulses (not
sufficient)
Now look toward Ultra MOV 14 mm series to selection :

Pulse Rating Curves for 14mm UltraMOV series
• In this case, we find that the UltraMOV can survive 2 to 10 pulses
So now go toward C-III series of littlefuse
Pulse Rating Curves for 14mm C-III series
• In this case, we find that the C-III can survive 10 to 100 pulses
So, how many pulses can 14mm C-III varistor take ?
Pulse Rating Curves for 14mm C-III series
• Consult the data sheet for verification of surge pulse capabilities
• From the table, the 14mm disc can survive 40 pulses
• So, the V150LA10C(P) is the best part for the requirements

Determine the peak voltage that the 3,000A surge will
create ?
Ar 3000A

V-I Curves for 14mm C-III series
• Consult the data sheet for verification of surge pulse capabilities
• From the table, locate the peak current on the x-axis (3,000A)
• Find where it intercepts the curve for V150LA10C(P) product
• In this case, the maximum voltage is found to be 850V
SECTION 2 CONTINUE…………………………..
- SELECTION OF MOV FOR LED LIGHTING
SOLUTION
- TVS DIODE SELECTION
- NTC SELECTION
- FINAL DEIGN LAST BARIER

THANKS REFERENCE 
- Protecting LED systems in accordance with IEEE & ANSI C62.41.2
- Philips Documentation
- Liitlefuse Documentation
- Bright king documentation
- Mouser Electronics
- CIRCUITS TODAY BLOGS
- WIKIPEDIA

JAYDEEP SHAH
ELECTRONICS COMMUNICATION ENGINEER
AHHMEDABAD INDIA
CONTCAT Me:
radhey04ec@gmail.com
FACEBOOK :
Shahjaydeep.jayshah

Surge protection with shah jaydeep

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