Technical info DKM - Terminology

Terminology

AC: Alternating Current

AC, which is different than DC, is the current coming from the power supply so that positive (+) pole and negative (-) pole can cross with regular time interval, and becomes current sine wave which the direction of current and voltage has regular period and is changed. In other words, this appears as if the pendulum swings from left to right with the constant rhythm.

DC: Direct Current

- DC is the current coming from the power supply that positive (+) pole and negative (-) pole are constant all the times, and the direction is invariable.
- The direction of voltage is constant
- DC generation device includes various rectifiers such as battery, storage battery, and DC generator

Frequency

- Frequency is the times of vibration that AC repeats for 1 second.
- The unit is HERTZ(Hz).
- In Korea, 60Hz frequency is employed as a standard which means that the direction of current changes from (+) to (–) 60 times for 1 second. At this time, the power stops temporarily and the lamp repeat on/off 120 times for 1 second. However, as AC flickers very fast, it is not possible to identify by the naked eyes.

Rating

- This means what is designed to be suitable for the requirements specified in the motor and when satisfied with the use conditions, the use limit is called ‘rating’.
- This designates voltage, current, rpm, frequency which determine the use limit for output. We call it rated output, rated voltage, rated current, rated rpm, and rated frequency.
- Rating includes continuous rating, short time rating, repeated rating and the induction motor manufactured by us is continuous rating and reversible motor is short time (30 minutes) rating.

1) Continuous Rating

When using continuously under the designated condition, if it is available to use continuously without exceeding the prescribed temperature rising and general condition, it is called ‘continuous rating’.

2) Short-time Rating

When operating during the prescribed time under the designated condition, if it is available to use without exceeding the prescribed temperature rising and general condition, it is called ‘short-time rating’. Short-time rating has 6 kinds of time: 5min, 10min, 15min, 30min, 1hr, and 2hr as a standard.

3) Intermittent Periodic Rating

When repeating Run and Stop periodically with constant load under the prescribed condition, if it is available not exceed general condition such as the prescribed temperature rising etc., it is called ‘repeated rating’.

Output

The thing which can be done by motor during the unit time and determined by rpm x torque.
The value of rated output is indicated as follows:

Output = 1.027xTxN [WATTS] Whereas,
T: TORQUE [kgf•m]
N: Number of rotation [rpm]
1 HP is 746 [WATTS]

Rated output

indicates the output which is generated continuously under the condition of designated voltage and frequency. This designated voltage and frequency is called the rated voltage and rated frequency. At this time, the rated output is called generally the output of motor

Torque and RPM

- Torque of motor is the revolution force to turn the body of revolution. The unit is [gf•cm] or [kgf•cm].
- The torque of 1kgf•cm is the revolution force when 1kg of force is applied to the right angle from the point of outer circle which radius of the body of revolution is 1cm

1) Starting Torque (① in Figure)

- This is the revolving force generated when motor starts and is called LOCKED ROTOR TORQUE or Starting Torque
If the bigger force than this torque is applied to the motor, the motor does not revolve.

2) Stalling Torque (② in Figure)

- The maximum torque of motor is Stalling torque.
- If there is a load more than maximum torque during operation, motor will stop.

3) Rated Torque (③ in Figure)

- It is the torque when the motor is the rated RPM.
- The torque when the rated output is generated continuously by applying the rated voltage to the motor.

4) Synchronous Revolutions (④ in Figure)

- It is RPM which is determined by the power frequency and the number of pole of motor.

NS=120f/P [rpm] Whereas,
NS: Synchronous RPM [rpm]
P: The number of pole of motor
f: Power frequency [Hz]
120: Constant number
rpm: Revolution per minute

Ex) If power frequency is 60Hz and motor has 4 poles,
NS=120*60/4=1,800[rpm]
And if power frequency is 50Hz and motor has 4 poles,
NS=120*50/4=1,800[rpm]

5) No load Revolutions (⑤ in Figure)

- It is RPM when motor revolves without applying any load to motor output shaft.
In this case, motor revolves low about 20~80[rpm] than synchronous rpm in Induction Motor or Reversible Motor.

6) Rated Revolutions (⑥ in Figure)

- It is RPM when rate rpm is generated by applying the rated load to the motor, and the most ideal RPM in use.

7) Slippage

- Slippage can be described in the following formula as one of the rotational speed.
S=(NS-N)/NS or N=NS*(1-S) Whereas,
NS: Synchronous RPM [rpm]
N: RPM at Temporary Load [rpm]
S: SLIP

Static Torque

It is torque which is generated when holding the load in the state that electric brake or clutch brake stops.

Permissible Torque

It is the maximum torque available when operating the motor. This is limited by rated torque of motor, temperature rising, and the strength of gearhead to combine.

Overrun

This is the angle (rpm) that indicates the excessive revolution of motor from the moment of power shutdown to the stop

Gear Reduction Ratio

- Gearhead is a speed converter using a gear and an instrumental device to reduce the rpm of motor into the required rpm and get bigger torque. Gear reduction ratio is a rate in which the gearhead decelerates the motor's rpm.
- There are two groups of gear reduction ratio; one is for 3, 5, 7.5, 12.5, 15... and the other is 3.6, 6, 9, 15, 18... which are 1.2 times the previous group so that you can obtain approx. the same output speed for both 50Hz and 60Hz.

Transmission Efficiency

- It is an efficiency with which motor torque is increased by the gearhead and described in %.
- It is determined by the bearing, friction of the gear tooth and resistance of lubricating oil.
- In general, this efficiency is approx. 90% per stage of the gear. If gear ratio is higher, the number of gear will increase and the efficiency rate will decrease.

Service Factor

- It is a coefficient which is used to estimate the service life of the gearhead.
- This value is generally derived from experience and based on type of the load and operating conditions.
- The life of a gearhead during particular application is estimated by dividing the standard life expectancy by the service factor.