• Inductance (L) and the drop caused by DC bias current:
  “Inductance” is the ratio of voltage to current-time gradient. (e = Ldi/dt) The purpose of measurement is to check permeability (μ), size, integrity of core and coil turn. The purpose of applying DC bias current is to check magnetic saturation characteristic of core.
• Quality factor (Q):
  “Quality factor” is the ratio of inductive reactance (X) to alternating-current resistance (ACR). (Q = X/ACR) About the purpose of measurement, please refer to “inductance” and “alternating-current resistance”.
• Direct-current resistance (DCR):
  “Direct-current resistance” is the resistance of copper wire. The purpose of measurement is to check soldering, wire material, coil turn, wire length, and wire breaking.
• Alternating-current resistance (ACR):
  “Alternating-current resistance” is the equivalent resistance including not only copper wire resistance but also hysteresis and eddy current losses. The purpose of measurement is to check copper wire and hysteresis, insulation characteristics of core material.
• Impulse winding test:
  “Impulse winding test” is a reliability test by analyzing the decay waveform caused by applying an unharmful, rapid, and low-energy impulse voltage across wound components. The purpose of test is to check lacquer and insulation material between turns and layers for detecting insulation fault.

Ground protection consists of two kinds of test method: Ground Continuity test (GC) and Ground Bond test (GB). The purpose of ground protection test is for protecting users from electrical hazards as touching equipment when unsuitable current is created and flows to the earth.

Please notice that may has difference between total current and real current cause by partly internal capacitive reactance. The current is outputting, if capacitive reactance is higher and reactive is higher, this makes real current lower relatively. If the user can’t measure output current accurately, it will cause a blind spot in testing.

DC hipot test usually need to add ramp time and fall time, because mostly DUTs are with capacitance and causes charging current generated(figure 3). For charging current steady, ramp time is needed for buffering then leakage current won’t over high because of charge current and judge as FAIL.

Because hipot test will cause DUT discharge, thus need a period of time for discharging after hipot test is ended. A fine hipot test equipment will descrease fall time to the minimum and mark danger warning before reaching discharge standard for protecting the testers from electrical shock.

The test voltage of standard is the mainly factor for judging good product in hipot test. A lot of hipot test equipment convert low voltage into high voltage by transformer then output it, but internal impedance of instrument will cause divider especially in some bad quality hipot test equipment, its actual output voltage can’t reach safety standard. For avoiding error to judge as good product and cause unnecessary trouble, fine hipot test equipment will auto gain compensation to modify and compensate voltage to needed voltage value and design the voltmeter on the output terminal for measuring accurately whether output voltage is insufficient.

All personnel of operating test equipment need to accept basic electronic theory training to realize the effect of current on human body and how to avoid electrical shock, familiar with test environment and precaution for emergency condition occurred. Some test equipments are with interlock function to prevent improper operation. When the personnel realize the previous described items then to explain operation procedure and test purpose about the condition of no good product and test fail occurred. Since the safety tests mostly are high voltage or mass current test, the test personnel should be pay more attention while testing.

The obvious answer is that products are regulated to protect consumers and operators from shock hazards. Shock hazards exist when a potential voltage and current are accessible to the operator with respect to earth ground. Electrical safety tests occupy very little time on the production line, but reduces the risks to operator and consumer considerably.

Almost all DUTs are equipped with a charged capacitor when testing DC Voltage. To avoid electrical hazards it is necessary to discharge the capacitor to a regulated voltage value at the end of the test. However, the higher capacitance value, the longer it takes to discharge, directly impacting the efficiency of the process. Our safety test equipment includes a fast and reliable capacitor discharge circuit to ensure production efficiency and safety.

The definition of medical equipment is the physical or electrical contact with patients (mostly regulations denotes human being, Europe regulations denotes human being and animal), applies to the equipment of diagnosing, treating and monitoring. The leakage current testing of medical equipment emphasizes on Applied part under normal using status by physical method to contact patient or accessories and facilities the patients need to touch such as probe, electrocardiogram, blood pressure bar and operating table. All types of leakage current will cause electrical hazards to patients and operators.

At the point of manufacture, before the product is available to the end user. Manufactures of electrical and electronic products need to insure that no hazardous voltages or currents are accessible to the user. They need to test their products to determine if they meet minimum safety levels. In order to do this, they need to test against a reference or standard.

Although the the dielectric withstand test and the insulation resistance test are similar, insulation resistance tests generally run below 1000 Vdc and return a value in ohms, while dielectric withstand test voltages can run up to 5000 Vac and 6000 Vdc depending on the requirements and returns a value in milliamps.

Patient leakage current consists of three kinds of test. The first test is the current flow from power terminal through applied part to earth terminal as product operating;Another test of patient leakage current, power source applies to MD by 110% the highest operating voltage. Make the current flows through applied part, accessible part then to earth terminal;The third test of patient leakage current, power source applies to SOP/SIP by 110% the highest operating voltage. When the product is operating, the current flows from two kinds of power terminal through applied part, MD then to earth terminal.

When the product is operating, the current flows from test point of applied part through MD to another test point of applied part then to earth terminal.

The current is brimmed over as flowing through insulation impedance we called it leakage current, contact by human body and the current through human body flow to Earth then electrical damage is occurred. The difference between leakage current test, withstanding voltage test and grounding protection test is equipment testing under running status. The leakage current adds a human body simulation impedance circuit in testing, it can simulate the quantity of leakage current through human body under real condition.

Insulation Resistance testing verifies the integrity of the insulation
by applying a DC voltage across the insulation and returns a value in Ohms
based on the applied voltage divided by the Leakage Current.

Flashover is an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. Vasily V. Petrov, a Russian scientist who discovered it in 1802, first described the phenomenon.

Obviously indicate that can’t occur breakdown in safety standard and partly safety standard request can’t occur Flashover/ARC(figure 4), and without definite test standard. ARC belongs to a kind of electrical discharge, when ARC occurred it means insulation capability insufficient. If ARC occurred several times then it will result in breakdown.

There are several different types of leakage current: Earth Line Leakage, Touch/Chassis (formerly Enclosure) Leakage, Patient Leakage, and Patient Auxiliary Current. The basic differences between leakage currents depend upon how a person might come in contact with the product or the measurement. For example the leakage that would flow through a persons body if they touched the outside enclosure of a product would be Touch/Chassis or Enclosure leakage.

Electrical shock and its effects can be caused and influenced by several factors. The primary effect is the result of electrical current passing through the human body. Severity of the injury to the human body is directly affected by such variables as: the nature of the electrical voltage (AC vs. DC); the pathway through the human body; conductivity of the contact (wet or dry); the size and shape of the individual involved (i.e., the person’s impedance), duration of the contact, and the size of the contact area. All these affect the magnitude of current that flows through the person’s body.

Studies have concluded that the human body can feel the sensation of an electrical shock with as little as 1.0ma of current. Since the human body is not a fixed resistance, the voltage required to produce 1.0ma of current can vary greatly based on the minimum impedance of the human body under various conditions (some models use a human body resistance value of 1K ohms up to 100K ohms).

Leakage Current is the residual flow of current through insulation after a high voltage has been applied for a period of time.  Earth Leakage Current is the leakage current from all earthed parts of the product. The current flowing from the mains supply through or across insulation into the Protective Earth Conductor.

The dielectric withstanding voltage of components depends on materials and the manufacturing process. For improving insulation in components, discharge levels should be defined including Corona discharge, Flashover and Breakdown. Chroma’s 19055 Hipot Analyzer is equipped with a Discharge Level Analysis mode (DLA) for defining the programming voltage, time, counts and limits of those three levels. DLA mode will indicate the withstanding voltage depending on the different level limit beginning with Corona Discharge Start Voltage (CSV), Flashover Start Voltage (FSV), and Breakdown Voltage( BDV). R&D and QC personnel are able to improve insulation by discharge data collection and analysis.

Dielectric Withstand or Hipot Testing can apply either an AC or DC voltage across the insulation and determines if there is leakage current or a Breakdown or ARC and returns a value in Milliamps.

Corona Discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient (the strength of the electric field) exceeds a certain value, but conditions are insufficient to cause complete electrical breakdown or arcing. Corona discharge may be an early symptom of an impending breakdown.

Breakdown is a rapid reduction in the resistance of an electrical insulator that can lead to a spark jumping around or through the insulator. This may be a momentary event (as in an electrostatic discharge), or may lead to a continuous arc discharge if protective devices fail to interrupt the current in a high power circuit.

The standard types of product safety compliance tests required today for most products are: Dielectric Strength (Hipot Test), Isolation Resistance, Leakage Current, Ground Continuity, and Ground Bond Tests. For a detailed explanation of electrical compliance tests, see Product Safety Tests in our Electrical Safety Testing Reference Guide.

Whatever national standard regulation or region standard regulation, the standard of leakage current is different by the insulation types of products. “CLASSI, II, III” are mainly in consideration of the insulation system of product which derived from IEC system, brief descriptions are as below:

• CLASS I indicates anti-shock protection of product not only depends on basic insulation but also includes grounding method.
• CLASS II indicates anti-shock protection of product not only depends on basic insulation but also includes additional precaution. For example double or reinforce insulation but without grounding or installation condition for relying precaution.
• CLASS III indicates anti-shock protection of product depends on power voltage is safety extra-low voltage (SELV) and it don’t generate danger voltage.

Determining the location of your test station is the first step in designing a safe and effective test station. The test station should be located away from traffic for the safety of anyone who may pass by the station and of course for the safety of the operator at the station. Limiting distractions to the test operator is an added step to ensure safety. The area should be marked with approved “DANGER – HIGH VOLTAGE” signs. The Hipot tester should have indicator lights to denote when high voltage is output. The test area should be separate from the assembly area.

A Ground Fault Interrupt (GFI) circuit that monitors the high voltage output and return line is an excellent operator and instrument safety feature. The current exiting the instrument’s high voltage output (Isource) is measured separately from the current flowing through the device under test (Idevice). To stop the flow of this extraneous current, the GFI circuit is employed to detect a current imbalance (as small as 250uA) between the output and return, then shut down the high voltage immediately. Chroma, distributed under the QuadTech brand, was the first company to maufacture a production hipot tester with a GFI circuit as standard.

The leakage current with different test mode by various safeties and different leakage current standard by various test point. The most often seen is that the current flows through DUT to E terminal of power, the human body touches E terminal of product will cause induction we called it earth leakage current. When earth leakage current is testing input 110% rated voltage to add human simulation circuit and judge if the current value of flowing through human simulation circuit is over the limit value of leakage current. In addition, there are Patient Leakage Current, Patient Auxiliary Leakage Current and etc leakage tests.

It may occur DUT no contact or bad contact condition during test procedure, especially in production line of emphasizing efficiency occurs more easily. The DUTs which are no contact, bad contact, test line damage or short circuit will judge no good product as good product or damage the equipment then cause the unnecessary risk cost. Thus, a lot of safety test equipment will judge if there is bad contact by low limit or high limit of current, this method interference factor too much so can’t judge effectively. The excellent safety test equipment filter short circuit DUT or judge circuit bad contact by more accurate judgment method (OSC) to save the production cost of manufacturers.

The insulation is divided into four types: Basic, Supplementary, Double and Reinforced. Because product inside may be over dirt, wet or other reason cause discharge along surface, thus judge if circuit design inside product has problems of distance along surface or insulation insufficiency by hipot test.

The first step in selecting safety test equipment is to understand your basic requirements. It may be the safety standard your product needs to comply to. The appropriate safety test equipment is not only selected in accordance with safety standards but considers functional product requirements, cost and efficiency. For example auxiliary accessories like HV Guns, fixtures, and software control can increase test efficiency. It is our recommendation to read Choosing the Right Test Equipment or give us a call to help select your equipment. 949-600-6400