Every machine is designed for particular voltage range. In between that stable range, Machine works precisely at maximum efficiency. Stable voltage also increases the overall useful life of machine. That’s why stable voltage is much important for machines.
In this post, We are going to discuss about the working of 25KVA Automatic Servo control voltage stabilizer made by Fuji Electric. If you want to know about its technical specifications, you can go through our previous post which based upon specifications of the stabilizer whose link been listed below:
Working principle of 25KVA ASC Voltage Stabilizer made by Fuji Electric
Transformer is the most important Electrical machine. Its primary function is; deliver the power from one circuit to another. While doing so it can produce a voltage difference at output side at same frequency. Transformer can step up & step down the voltage easily. It is the efficient Electrical machine without any moving part. That’s the reason Transformer is most widely used around the world.
You may think off why I’m talking about transformer in this post but Transformer is the main component behind the working of servo control voltage stabilizer. Which we are going to discuss next. A ‘Buck boost transformer’ is behind the working servo voltage stabilizer.
In this voltage stabilizer, Three phase input supply is divided into 3 individual phases. Every single phase of three phases stabilize individually that’s why for all the three phases, there are three buck-boost transformers.
Each controllable phase is passing through HV or secondary side of Transformer in a series. If a variation of voltage is applied at primary; which is primary; it produces proportional variation on HV side.
” In a Transformer , a voltage variation on primary side produces similar variation on secondary side. If voltage on primary side increases, voltage on secondary side increases proportionally. Similarly, the case when voltage decreases on primary, voltage decreases on secondary proportionally. “
For an Example:
Let suppose, A 500KVA Transformer with 11kV/415V Voltage ratio.
HV/primary voltage is 11KV
LV/secondary voltage is 415V
Voltage ration becomes 11÷415=26.5
When voltage on primary side decreases to 10kV than voltage on secondary becomes 10kV÷26.5= 377.3V
When voltage on primary side increases to 11.5 KV than voltage on secondary becomes 11.5KV÷26.5=433.9V }}
25KVA automatic servo voltage stabilizer by Fuji
” Application of voltage variation of Transformeris used in this servo voltage stabilizer. “
Step-by-Step Working of servo control voltage stabilizer
Input voltage is sensed continuously
Control card compares with reference voltage
If voltage is low → servo motor rotates to boost
If voltage is high → motor rotates to buck
Variac changes transformer input
Buck-boost transformer corrects output
Output maintained at 415V
Parts of the Stabilizer
In this machine, like other Electrical machines, There is two type of wirings:
Power wiring
Control wiring
We are going to explain power wiring & its components first; after that we will explain control wiring.
1. Power Wiring & it’s components
Power wiring as name implies heavy load current flows through this wiring. Since heavy current flows through this wiring that’s why heavy wires & heavy components are used in this wiring. We will explain the wiring step by step, starting from the input.
Input/Output terminals
Input/Output terminals are provided at the back down side of stabilizer. Earth+3phase+neutral inputs/outputs are connected at these terminals. Shown in an image below:
INPUT/OUTPUT Terminals | 25KVA automatic servo voltage stabilizer by Fuji
Input supply then connected to the 3pole 50Amps MCB. MCB provides protection in short circuit conditions.
MCB & BYPASS SWITCH | 25KVA automatic servo voltage stabilizer by Fuji
Buck boost Transformers
From the output of MCB, all the 3phases gets divided into 3 individual single phases. Voltage rectification is done on all the 3phases individually that’s why 3 Buck boost transformers are used. Each Phase is connected to the secondary of buck boost transformer in a series manner. shown in an image below :
Transformer secondary conductor is thicker in size as compare to primary conductor because load current flows at secondary. While control current flows at primary.
Buck-Boost Transformer | 25KVA automatic servo voltage stabilizer by Fuji
Three phases from all the three buck boost transformer are connected to the 3pole contactor. Contactor works when control card gives signal to the Contactor . When everything is in permissible limit, control card energies the Contactor & supply becomes available at output side of Contactor .
Contactor MI50 by L&T | 25KVA automatic servo voltage stabilizer by Fuji
Changeover Switch
Changeover switch provides function of ‘bypass’, ‘switch off’ & ‘stabilized voltage’. Changeover has 3 points at which 3phase rectified output supply from Contactor , 3phase direct input supply & output terminals are connected.
Changeover Switch | 25KVA automatic servo voltage stabilizer by Fuji
We can connect the output terminals with servo stabilized voltage by selecting changeover at SCVS or we can connect the output directly with input by selecting the changeover switch at BYPASS or we can disconnect the output terminals at 0 point of changeover.
Control Wiring & it’s Components
Control wiring has further multiple components which are briefly discussed next !
HMI
This servo contains HMI with small display for checking of voltage on both Input & Output sides. HMI is also utilized to display load current & frequency.
HMI ASC Voltage stabilizer | 25KVA automatic servo voltage stabilizer by Fuji
We can also switch ON & switch OFF the stabilizer output through this HMI. It also displays the error logs on display.
Parameters & setting changes, all can done with the help of this HMI.
Control Card
It is Brain of the stabilizer. It continuously monitors voltages on both the Input & Output sides.
It takes feedback from output voltage & produces variation to meet the pre-set value.
Control Cards | 25KVA automatic servo voltage stabilizer by Fuji
” Phase reversal protection, protection from single phasing, neutral failure protection, Earth-Neutral voltage cut of – all the protection commands are produced by the control card. “
Variac & it’s Components
Principle of operation of stabilizer; explained above. It’s an action of buck boost transformer on which load current passes through the secondary of the Transformer in a series configuration. Changes on secondary occurs when changes occurs on primary side.
Symbolic representation of variac
Primary of Transformergets control supply through a Variac such that a carbon brush arrangement moves on variac with the help of single phase rugged AC synchronous motor along with gear system.
This servo motor is slow speed high torque motor. It start & stop instantly. It is 230Volts, 27Watt motor. It runs at a speed of 60 rpm. An RC (Resistance & capacitor) circuit for motor functioning has been provided with the motor.
Variac | 25KVA automatic servo voltage stabilizer by Fuji
Servo motor | 25KVA automatic servo voltage stabilizer by Fuji
This motor is capable of rotation in both forward & reverse directions. Command of movement ‘how much & in which direction‘ to servo motor is given by triac PCB. Triac printed circuit board is actually work as a relay card upon which 6 switch components are present. These relay cards get supply from control card.
Variac with Servo motor | 25KVA automatic servo voltage stabilizer by Fuji
Each switch components operates the motor in one direction but we need to rotate the motor in both the directions that’s why we need 2 switch components for single motor. These components are control switches which switches the servo motor according to the command of main control card.
To Limit the movement of carbon brushes on variac, micro limit switches have been installed. These micro switches are installed on both the ends of variac. Command wire to servo motor is actually in series with the NC point of the limit switch.
Micro limit Switch | 25KVA automatic servo voltage stabilizer by Fuji
This is all about the working of automatic servo control voltage stabilizer.
Advantages of Servo Stabilizer
High accuracy (±1%)
Smooth voltage correction
Suitable for industrial loads
Protects motors, CNC, machines
High efficiency (>98%)
FAQ
Q1. What is the output voltage of a 25 kVA servo stabilizer? 415V three-phase.
Q2. How fast does a servo stabilizer correct voltage? It corrects voltage continuously within seconds using a servo motor.
Q3. Why buck-boost transformer is used? To increase or decrease voltage as per requirement.
Q4. Is servo stabilizer better than static stabilizer? Yes, for heavy industrial loads due to higher accuracy and capacity.
Q5. How many stabilizers are inside a three-phase servo? Three single-phase stabilizing units (one for each phase).
SUMMARY
This post explains the workings of the 25KVA Automatic Servo Control Voltage Stabilizer by Fuji Electric. It emphasizes the importance of transformers, specifically the buck-boost transformer, as crucial components in voltage stabilization. The stabilizer ensures that each phase of a three-phase supply is stabilized individually using separate transformers. A detailed overview of power and control wiring is provided, alongside the roles of various components such as the MCB, contactors, and HMI for monitoring. The post concludes by inviting reader questions and feedback.
Hope! You like the post. If you have any doubt, suggestion or query please do comments. Your comments are valuable to us.
