K8AK-AS

8

Checking Operation

Overcurrents

Gradually increase the input from 80% of the set value.

The input will equal the operating value when the input

exceeds the set value and the alarm indicator starts flashing.

Operation can be checked by the relay outputs that will start

after the operating time has passed.

Undercurrent

Gradually decrease the input from 120% of the setting and

check the operation using the same method as for

overcurrent.

Example: Overcurrent Operating Mode, Normally Open Relay Drive,

and an Operating Time of 5 s

Connection Diagram

How to Measure the Operating Time

Overcurrent

Change the input suddenly from 0% to 120% of the set value

and measure the time until the Unit operates.

Undercurrent

Change the input suddenly from 120% to 0% of the set value

and measure the time until the Unit operates.

Monitoring Switch-mode Power Supplies

Switch-mode Power Supplies cannot be monitored. In circuits

with a capacitor input, including switch-mode power supplies,

the input capacitor recharge current flows in pulse form as the

load current. The K8AK-AS

@ has a built-in filter as a

countermeasure against high frequencies and cannot be

used to remove pulse current.

Can a motor with a rated current of 5 A be

monitored using the K8AK?

Are there any application precautions?

The K8AK-AS1 and K8AK-AS2 cannot be used with motor

loads. Use the K8AK-AS3 in combination with the K8AC-

CT200L Current Transformer (CT). With motor loads, the

startup current and stall current will cause a current of many

times the rated current to flow. Refer to the following figure for

information on the motor startup current.

For a motor with a rating of 5 A, the startup current will be

approximately 30 A. The startup current will exceed the

overload capacity (rating: 150% for 1 s) of the K8AK-AS1 and

K8AK-AS2 and result in failure of the Relay.

To monitor the motor load, use the K8AK-AS3. (Overload

capacity: 120% of rating for continuous load, 200% of rating for

30 s, and 600% of rating for 1 s).

The K8AK-AS3 has a large input range. Pass the conductors

multiple times through the special CT.

Concept behind Passing Conductor through the CT When

Using the K8AK-AS3

Example: Monitoring Overload of a Motor with a Rated Current of 5 A

K8AK set value:

Overcurrent detection, operating value setting: 25%, operating time: 0.1 s

Startup lock timer: 0.1 to 30 s (Set the timer according to the duration of the

startup current.)

The setting range for the K8AK-AS3 is 10% to 100% of the rated

current (i.e., 10 to 100 A). Pass the conductors through the CT five

times so that at least 10 A of current flows. The input current to the

K8AK will be 25 A (i.e., 5 A x 5 loops).

If a startup current of six times the rated current is generated, it will be

150 A (i.e., 25 A x 6). The overload capacity for the K8AK-AS3 is

200% of the rating for 30 s. The Relay will not fail even if the startup

current continues for 30 s, and it is possible to perform overload

detection.

Questions and Answers

Q

Set value

Current input

Alarm indicator

Relay output

Flashing

Lit

5 s

100 VAC

100 VAC

30

Ω

0 to 10 A

A

A1

A2

±

C 100 V

Variable autotransformer

Input terminals

Power

supply

Output

Cycle counter

400 W (two in parallel)

Q

Q

Q

Several seconds to

several tens of seconds

Time from beginning of startup

100%

500%

K8AC-CT200L

Primary-side conductor

To the K8AK-AS3