The document discusses automatic transfer switches (ATS). An ATS automatically switches power sources to ensure reliable electrical supply to connected loads. It will start a backup generator and switch over to it upon sensing a failure of the primary power source. When the primary power is restored, the ATS will switch back and shut off the generator. ATS are commonly used in homes with backup generators to power the home during utility outages. They isolate the generator from utility lines for safety and prevent overloading. The document describes different types of ATS including open transition, closed transition, soft loading, and static, as well as their applications.

1. Automatic Transfer Switch (ATS)
EE 50 – ELECTRICAL EQUIPMENT
AND DEVICE
MARK ANTHONY B. ENOY
BS EE - V
ENGR. KARRLOU C. RODA
INSTRUCTOR

2. Transfer Switch
A transfer switch is an electrical
switch that switches a load
between two sources.

3. Manual transfer switch
Automatic Transfer
Switch

4. Manual transfer switch
- an operator affects the
transfer by throwing a switch.

5.  Automatic Transfer Switch
- An ATS is a device designed to
Automatically switch (transfer)
between (2 or 3) sources of power to
improve the reliability of the
electrical supply to a connected
load.
- It automatically switches when
it senses one of the sources has
lost or gained power. Current
range up to 4000 Amperes.

6. Automatic Transfer Switch

17. Operation of an Automatic Transfer Switch
Not only does ATS transfer the
load to the backup generator but
also it commands the backup
generator to start, based on the
voltage monitored on the primary
supply.

18. Example: ATS installed in homes
In a home equipped with a backup
generator and an ATS, when an electric
utility outage occurs, the ATS will tell
the backup generator to start. Once the
ATS sees that the generator is ready to
provide electric power, the ATS breaks
the home's connection to the electric
utility and connects the generator to the
home's main electrical panel.

19. Example: ATS installed in homes

20. Example: ATS installed in homes
The generator supplies power to the
home's electric load, but is not
connected to the electric utility
lines. It is necessary to isolate the
generator from the distribution
system to protect the generator
from overload in powering loads
beyond the house and for safety, as
utility workers expect the lines to
be dead.

21. Example: ATS installed in homes
When utility power returns for a
minimum time, the ATS will
automatically transfer the house
back to utility power and
command the generator to turn
off, after another specified
amount of "cool down" time
with no load on the generator.

22. Typical Applications of ATS

23.  Utility and Engine Generator
- Single unit standby applications
are very common
For facilities with a standby power
system and a single utility feed. The
transfer switch senses when utility
power has been lost, sends a start
signal to the standby generator and
transfers the load.

24. Utility and Engine Generator

25.  Utility and Utility
- Dual utility applications are
becoming more common
For use in facilities with redundant
utility feeds but no standby
generator. If one utility feed fails,
the transfer switch automatically
connects the load to the second
utility feed.

26. Utility and Utility

27.  Generator and Generator
- Prime power / standby application
For facilities with a prime power
system
using
multiple
on-site
generators. If the primary generator
fails, the transfer switch sends a start
signal to the second generator and then
transfers the load.

28. Generator and Generator

29.  Three-source system
For facilities with a standby power
system and two utility feeds. The
utility transfer switch controls the
feeds from the two utilities based on a
pre-established priority. If both utility
feeds fail, the generator transfer
switch sends a start signal to the
standby generator and transfers the
load.

30. ONE STANDBY POWER SYSTEM AND TWO UTILITY FEEDS

31. Three-source system :
Another three source system uses a
standby generator in place of the
second utility (dual standby). If the
utility fails, the first transfer switch
sends a start signal to the primary
standby generator and transfers the
load. If the primary standby generator
fails, the transfer switch sends a start
signal to the second generator set and
transfers the load.

32. TWO STANDBY POWER SYSTEM AND ONE UTILITY FEEDS

33. Types of ATS Transition
Open transition TS
Closed transition TS
Soft loading TS
Static TS

34. Open transition TS
An open transition transfer
switch is also called a break
before make transfer switch.
A break before make transfer
switch breaks contact with one
source of power before it makes
contact with another.

35. It prevents backfeeding from an emergency
generator back into the utility line
Backfeeding occurs when electric power is
being induced into the power grid. Power
flows in an opposite direction.
It can cause utility lineman to be
electrocuted as they work in power lines.
Reverse- power relay opens if backfeeding
occurs in the power lines.

36. Applications: Emergency, coderequired and optional standby
systems; resistive loads; small
motor loads

38. Open transition TS:
o Knife Blade Switch




Typically Non-Load breaking
Usually Manually Operated
Sometimes motor operated - Is a method of
arc suppression
Low withstand ratings – no
that extinguishes
arc chutes or vents
arcs by
 Low endurance ratings
channeling them
limited life
into chambers
- arc flash happens when electric current
flows through an air gap between
conductors.
above the
contacts.

39. Closed transition TS
A closed transition transfer switch is
also called a make before break
transfer switch.
A make before break transfer
switch makes contact with another
source before it breaks contact with
the interrupted source.

40. There are some loads, however,
that are affected by even the
slightest loss of power. There
are also operational conditions
where it may be desirable to
transfer loads with zero
interruption of power when
conditions permit.

41. For
these
applications,
closed transition transfer
switches can be provided.
With
closed
transition
transfer, the on-site engine
generator set is momentarily
connected in parallel with
the utility source.

42. This
requires
getting
approval from the local
utility company. The switch
will operate in a makebefore-break mode provided
both sources are acceptable
and synchronized.

43. Typical parameters determining
synchronization are:
•voltage difference less than 5%
•frequency difference less than 0.2 Hz
- Frequency counter is used to measure frequency
•maximum phase angle between the
sources of 5 electrical degrees
- Is the difference between the phase of a
sinusoidally varying quantity and the phase
of a second quantity which varies
sinusoidally at the same quantity.

44. Analog Voltage & frequency meter
Digital Generator Frequency & Voltage meter

45. Closed
Transition
(Make-BeforeBreak Operation)
NOTE: “P” Position indicates
both sources paralleled for 5
cycles
Applications:
Critical power
requirements,
including
hospitals and
data centers

46. Delayed Transition (center off)
- The delayed transition (center off) switch is
especially suited to applications in which large
inductive loads result in large inrush currents.
The delayed transition allows magnetic fields to
completely collapse before reconnection.
- A time delay between the opening of the
closed contacts and the closing of the open
contacts allows large motor loads to
demagnetize before transfer. This prevents the
severe “bump” caused by switching a rotating
motor (which momentarily acts as a
generator) from one source to another source
that is not in synchronism.

47. Types of ATS
Construction &
Design

48. Knife
Blade
Type
Twin
Contactor
Type
Twin
MCCB
Type
Power
Contactor
Type
Static
Transfer
Type

49. Knife Blade

50. Closed transition TS
o Twin Contactor
- contactor type is simpler design that is electrically operated
and mechanically held. It operates faster than circuit breaker
transfer switches, which reduces transfer time.







Switching device having 1 position of rest
Returns to position of rest @ loss power (un-latched type) or
add’l latching arrangement to hold position on loss of power
Built using 1 of up to 12 types of contactors under, from
basic contactor to high-capacity motor starters.
Often very basic controller
Mechanical/safety interlock often not available or optional
Variety of operators, from motor to electromagnets
Not a True double throw device - possible to close into both
Sources

51. Twin Contactor

52. Closed transition TS
o Twin MCCB (Molded Case Circuit Breaker)
- circuit breaker type has two interlocked circuit breakers,
so only one breaker can be closed any anytime.






2 Position device, typically operated from add-on motors
Built using 1 of up to 2 types of breaker under, from basic
instantaneous-trip type to short-time rated devices.
Mechanical/safety interlock is an add-on, sometimes
optional
Motor operators usually slow, often unreliable for high duty.
Wide range of manf-assigned withstand ratings (low, med,
or high)
Not a True double throw device - possible to close into both
Sources

53. Twin MCCB (Molded Case Circuit Breaker)

54. o Power Contactor Type
 Std. Double Throw mechanism - Inherent
mechanical interlock against closing to
both sources
 No add-on interlocks required
 Fewer moving parts
 High Withstand Current ratings to allow
fault clearing coordination
 Integrated Arc quenching components
 Solenoid Operated (very fast)

55. Power Contactor Type

56. o Power Contactor ATS - Composition
•
•
•
•
•
•
Arc quenching grids & enclosed arc chutes
Movable contact assembly has 2 pieces, arcing contact
and main current carrying contact.
Arcing contacts make first, break last
Silver alloy contacts
 Resists welding
 Enhanced withstand ratings
“Over center” switching principal to achieve a
mechanically locked position in either Source 1 or 2
High speed solenoid actuated drive assures contact
transfer in 30-50 msec

57. Power Contactor ATS - Composition

58. Static/ Solid-State Transfer Type
The static/solid-state ATS lacks the traditional
mechanical transfer switch. Because this unit relies
on SCR or transistor technology, sub-cycle transfers
are possible. Although there is technically a "break"
in load current, the speed of these units prevents
adverse effects to sensitive equipment.

59. Static Transfer Type






Two live sources required. Solid-state
switching >> no moving parts
Extremely FAST operation, transfer in
less than ¼ cycle.
SCR technology
Typically used on critical loads where 2
reliable and independent power
supplies available, or switching 2 x UPS
Outputs.
Both sources must be in sync
Often cost prohibitive for Standby
applications
E
N
2
1
L

60. Static Transfer Type

61. Bypass Isolation Transfer
Allows maintenance to the main
ATS without disconnecting the
load. By having two transfer
switches connected in parallel, the
bypass transfer switch adds
redundancy to the system.
Applications: Critical power and maintenance
requirements, including healthcare and data
center

62. Bypass Isolation ATS
• Essentially (2) ATS in Parallel, (1)
Automatic Switch (ATS) & (1) Manual
Switch (MTS).
• ATS is withdrawable, similar to
withdrawable CB’s
• (2) redundant paths from each source
to load.
• ATS & MTS are mechanically and
electrically interlocked
– To prevents accidental closure of
both sources
• Bypassing power from Source to Load
permits testing or maintenance of ATS
without interruption to load.
• Available in Open, Delayed, and
Closed Transition
• If power fails while bypassed, Genset
is auto started to permit fast transfer
using MTS.
TWO PATHS FROM
SOURCE TO LOAD
WITHDRAWABLE
ATS
MECHANICAL
INTERLOCKS
FIXED MOUNT MTS

63. Thank You!

65. CREATIVE MAKER:
MARK ANTHONY B. ENOY
BS EE – 5

66. SPECIAL THANKS TO MY SPONSORS: