ELEC5205 Chap.6 AC, DC and Impulse Test Sources
AC, DC and Impulse Test Sources
Waveform selects the source
High-voltage tests investigate service withstand, design performance or ultimate strength. Cascaded transformers add AC stage voltages, while resonant testers use a capacitive test object and circuit Q to create high voltage with modest source power. Rectifier multipliers produce high DC with ripple and regulation limits.
Single-stage and Marx impulse generators discharge stored capacitor energy through shaping resistors to reproduce fast-front transient stress.
Separate voltage creation from energy delivery
A source can reach the required terminal voltage yet still be unsuitable for the load. A long cable is strongly capacitive, so a direct power-frequency source must supply a large reactive current.
Series resonance cancels that current locally and lets the supply cover losses, while a cascade raises AC voltage by stacking transformer stages at progressively higher potential.
In either case, state rms or peak convention, test-object capacitance, required duration and available fault energy before calculating a rating.
Read multiplier performance as a loaded problem
The ideal DC multiplier relation describes the no-load stacking action. Under load, charge is removed between charging intervals and must be replenished through finite capacitors and rectifiers.
Ripple and regulation therefore worsen with current and stage count. A useful answer distinguishes ideal output from loaded output, identifies which column smooths the voltage, and checks component peak inverse voltage.
Reversing polarity or changing frequency alters insulation and charging requirements even if the nominal DC magnitude stays fixed.
Build an impulse from stored energy and time constants
An impulse generator first stores energy in capacitors, then changes the connection for rapid discharge. A Marx network charges stages in parallel and discharges them effectively in series after gap firing.
Front resistance mainly controls the fast rise, while tail resistance and the effective load capacitance shape the slower decay. The test object is part of that network, so replacing it can change the waveform.
Report front and tail quantities with their defined time conventions rather than describing the trace only as fast or slow.
Use a source-selection audit
Begin with the stress being represented: continuous AC, essentially steady DC, or a transient impulse. Next identify the load, voltage basis and required measurement bandwidth.
Then compare power, stored energy, regulation, waveform tolerance and behaviour after insulation failure. A resonant arrangement may limit follow-through energy by losing tune, whereas a large charged capacitor can deliver substantial local energy. Finish by naming the measurement that proves the specified waveform actually reached the object; the circuit diagram alone is not test evidence.
What this chapter covers
- 01
Cascaded Transformers
- 02
Series Resonance
- 03
Voltage Doubler
- 04
DC Multiplier
- 05
Impulse Shaping
- 06
Marx Generator
Worked example · free
Check a resonant tester
- 2Multiply feed voltage by Q for ideal test voltage.
- 3Divide circulating reactive power by Q for approximate losses.
- 2Explain resonance collapse when the object fails.
Key terms
- Series Resonance
- Series Resonance is the tuned condition where inductive and capacitive reactances cancel and the test-object voltage is magnified by circuit Q.
- Voltage Multiplier
- Voltage Multiplier is a rectifier-capacitor network that stacks charge-pump stages to produce high DC voltage.
- Marx Generator
- Marx Generator charges capacitor stages in parallel and connects them effectively in series during an impulse discharge.
AC, DC and Impulse Test Sources FAQ
Why is resonance useful for testing cables?
A long cable is strongly capacitive. Tuning a reactor against that capacitance produces a high test voltage while the supply covers mainly losses, so required source power is far below the reactive power circulating in the test circuit.
Why is a multiplier output below its ideal value?
Load current, capacitor leakage and finite rectifier resistance discharge the stages between charging intervals. The result is ripple and voltage drop, so the ideal twice-stage-count-times-input-peak expression is an unloaded reference.
What controls an impulse waveform?
Stored capacitance, load capacitance and the front and tail resistances set the rise and decay. Changing the test object changes effective capacitance, so resistor values may need adjustment to retain the specified waveform shape.
Exam move
Classify each source by AC, DC or impulse waveform and by the test-object load. Practise the rms-to-peak conversion, one Q-factor calculation and one ideal multiplier calculation. Draw charging and discharge states separately for the Marx network so series and parallel connections do not become confused.
Add a selection ledger with columns for waveform, load capacitance, source power, stored energy, regulation and failure behaviour. For every numerical result, state whether it is an ideal capability or a loaded value. Finish by sketching where voltage is measured and which divider bandwidth is needed to verify the applied wave rather than merely the generator setting.
Recheck one design after changing load capacitance, because tuning, impulse time constants and delivered voltage all respond to the connected object.
Working through AC, DC and Impulse Test Sources in ELEC5205? Sia is AskSia’s AI Electrical Engineering tutor — ask any ELEC5205 AC, DC and Impulse Test Sources question and get a clear, step-by-step explanation grounded in how ELEC5205 is taught and assessed. Read this chapter free, then take your hardest questions to Sia.
