What is a Swinburne’s Test : Calculations & Its Applications
The simple and indirect method of testing DC machines with constant flux is Swinburne’s test of DC shunt and compound wound DC machines. It is named as Swinburne’s test after Sir James Swinburne. This test helps to pre-determine the efficiency at any load with constant flux. The most important advantage of Swinburne’s test is, the motor can be used as a generator and no-load losses can be measured separately. This test is very simple, and economical because it operates in no-load power input. This article describes the Swinburne’s test of DC machines.
What is Swinburne’s Test?
Definition: The indirect test used in the measurement of no-load losses separately and pre-determination of efficiency at any load in advance with constant flux on the compound and shunt DC machines are called Swinburne’s test. Mostly this test is applied for large shunt DC machines for efficiency, load losses, and temperature rise. It can also be called a no-load loss test or load loss test.
Swinburne’s Test Theory/Circuit diagram
The circuit diagram of Swinburne’s test is shown below. Consider that, the DC machine / DC motor runs at rated voltage with no-load input power. However, the speed of the motor can be regulated using the shunt regulator as shown in the figure. The no-load current and the shunt field current can be measured at the armatures A1 and A2. To find the armature copper losses, the resistance of the armature can be used.
Swinburne Test of DC Machine
Using the Swinburne’s test, the losses occurred in DC machines can be calculated with no-load power. Since DC machines are nothing but motors or generators. This test is applicable only for the large shunt DC machines which have constant flux. It is very easy to find the efficiency of the machine in advance. This test is economical because it requires a small input power with no-load.
Swinburne Test on DC Shunt Motor
The Swinburne’s test on DC shunt motor is applicable to find the losses in the machine with no-load power. The losses in the motors are armature copper losses, iron losses in the core, friction losses, and winding losses. These losses are calculated separately and efficiency can be pre-determined. As the output of the shunt motor is zero with no-load power input and this input no-load is used to supply the losses. Since the change in iron losses cannot be determined from no-load to full-load and the change in temperature rise cannot be measured at full load.
Calculations
Swinburne’s test calculations include calculation of efficiency at constant flux and losses of the DC machines. From the above circuit diagram, we can observe that the DC machine/DC shunt motor runs at rated voltage with no-load. And the speed of the motor can be controlled using the variable shunt regulator.
At no-Load
Consider, the no-load current is ‘Io’ at armature A1
Shunt field current measured at Armature A2 is ‘Ish’
The no-load armatures current is the difference between no-load current and shunt field current at A2, given as = (Io – Ish
The input power at no-load in watts = VIo
The equation for armature copper losses at no-load power input is, = ( Io – Ish ) ^2 Ra
Here Ra is the resistance of the armature.
The constant losses at no-load are the subtraction of armature copper losses from the no-load input power.
Constant losses C = V Io – ( Io – Ish )^2 Ra
At Load
The efficiency of the DC machine/ DC shunt motor at any load can be calculated.
Consider the load current I, to determine the efficiency of the machine at any load.
When the DC machine acts as a motor, the armature current Ia = ( Io – Ish )
When the DC machine acts as a generator, the armature current Ia = ( Io + Ish )
Input power = VI
For DC motor at on load:
Armature copper losses are Pcu = I^2 Ra
Pcu = ( I – Ish )^2 Ra
Constant losses C = VIo – ( Io – Ish )^2 Ra
Total losses of the DC motor = armature copper losses + constant losses
Total losses = Pcu + C
Hence the efficiency of the DC motor at any load is, Nm = output/input
Nm = ( input – losses ) / input
Nm = ( VI – ( Pcu + C ) ) / VI
For DC Generator on Load
Input power at no-load = VI
Armature copper losses = Pcu = I^2 Ra
Pcu = ( I + Ish )^2 Ra
Constant losses C = VIo – ( I – Ish )^2 Ra
Total losses = armature copper losses Pcu + Constant losses C
Hence the efficiency of the DC machine when it acts as a generator at any load is
Ng = output / input
Ng = ( input – losses )/ input
Ng = ( VI – ( Pcu + C ) / VI
These are the equations for no-load losses and the efficiency of the DC machines at any load.
Difference between Swinburne’s Test and Hopkinson’s Test
The difference between these two is discussed below.
Swinburne’s Test |
Hopkinson’s Test |
It is an indirect method of testing DC machines. | It as a regenerative test or back-to-back test or heat run test of DC machines |
It is used to find efficiency and no-load losses. | It is also used to find efficiency and no-load losses. |
It is applicable for large shunt machines at a no-load input power | It is applicable for large shunt machines at a no-load input power |
Only one shunt machine is used. During this test, the DC machine runs as a motor or generator for only one time. | Two shunt machines are uses one acts as a motor and another one acts as a generator |
It is very simple and economical. | It is very economical and difficult to perform because two shunt machines are used. |
It is very difficult to find commutation conditions and temperature rise at full-load. | It is very easy to find the temperature rise and commutations at any load with rated voltage |
Efficiency can be pre-determined at any load | It is also used to find efficiency and no-load losses. |
Swinburne’s Test Applications
The applications of this test include the following.
- This test is used to find efficiency and no-load losses of the DC machines at constant flux.
- In DC machines when runs as motors
- In DC machines when runs as generators
- In large shunt DC motors.
Swinburne’s Test Advantages & Disadvantages
The advantages of this test include the following.
- This test is very simple, economical and most commonly used
- It requires no-load power input or less power input when compared to Hopkinson’s test.
- Efficiency can be determined in advance because of the known constant losses.
The disadvantages of this test include the following.
- The change in iron losses from no-load to full-load cannot be determined because of the armature reaction
- It is not applicable for DC series motors
- Commutation conditions and temperature rise cannot be checked at full-load with the rated voltage.
- It is applicable for the DC machines which have constant flux.
Thus, this is all about Swinburne’s test – definition, theory, circuit diagram, on DC machines, on DC shunt motor, test calculations, advantages, disadvantages, applications, and the difference between Hopkinson’s test and Swinburne’s test. Here is a question for you, ” What is Hopkinson’s test of DC Shunt motors?