Two-Branch Measurement Method

flux

Below is some feedback on your current schematic and suggestions to ensure the two‐branch method works correctly for determining the unknown insulation resistance (Rx):

Table

ComponentRoleComments and Suggestions
High Voltage Source (HV_1000V)Supplies 1000 VDCVerify that the high‐voltage source is isolated and that all high‐voltage connections are properly rated.
Reference Resistor (R1)Known resistor in the voltage dividerEnsure its value is chosen for a good measurement range (e.g., 1 MΩ). Confirm that its high‐voltage rating meets 1000 VDC.
Insulation Resistor (Rx)Unknown resistor (insulation under test)Its value should be very high (typically many MΩ), not something like 500 Ω. Adjust Rx to the expected range.
Other Resistors (R0, R2)Currently present in your schematicThey appear to be interfering with the intended two‐branch divider. For the insulation meter, use only R1 (reference) and Rx.
Op-Amp (Voltage Follower)Buffers the measurement nodeConfirm that the op-amp’s input and supply are properly isolated from the high-voltage branch. Decoupling is critical.
Decoupling Capacitor (C1)Stabilizes the op-amp supplyVerify its placement between the op-amp supply and ground.
Key Points to Address:
  1. Voltage Divider Arrangement:
    • Ideally, only two elements should form the divider: the known resistor (R1) and the unknown insulation resistance (Rx).
    • The test voltage from HV_1000V should connect to R1, then the junction between R1 and Rx is buffered by the op-amp, and finally, Rx goes to ground.
  2. Component Values:
    • The value of Rx must be compatible with your expected insulation resistance range (typically in the tens to hundreds of MΩ). A value of 500 Ω is far too low for insulation measurements.
    • Adjust the reference resistor R1 (if needed) so that the voltage at the divider gives you a measurable output without overdriving the op-amp input.
    • Ensure that all resistors, especially those in the high-voltage branch, are rated for 1000 VDC.
  3. Net Connectivity and Airwires:
    • Your review errors (airwires between Rx and R1, etc.) indicate that some nets might not be correctly connected.
    • Double-check the connections so that:
      • The HV source connects only to R1.
      • The junction between R1 and Rx is the sole measurement node.
      • No additional resistors (like R0 or R2) interfere with this node.
Next Steps:
  • Review and modify your schematic to remove or reassign R0 and R2 if they are not part of the measurement branch.
  • Update Rx to a value consistent with insulation resistance (high value, e.g., tens of MΩ).
  • Rewire the voltage divider so that there is a clear path from HV_1000V → R1 → measurement node → Rx → Ground, and then buffer the node via the op-amp.
Would you like to adjust the schematic now to implement these changes? If so, I can provide a step-by-step suggestion to update your project.
Adjust Rx value
Remove R0 and R2
Rewire schematic
i am talking about this schematic
jetpace

jetpace

@copilot i am talking about this schematic
1y

copilot

Got it! You're referring to the schematic in the provided project description. How can I assist you with it? Do you have any specific questions or modifications in mind?
1y
jetpace

jetpace

values of resistors is it okay ESC of Rx ?
1y

copilot

In your schematic, you have the following resistors:
The resistor Rx, with a value of 100 Megaohms, is relatively high. If you’re considering the electric strength (or voltage rating) for Rx, standard SMD resistors like the 0603 package typically have voltage ratings around 50V. However, it would be essential to verify the specific part's datasheet, as the voltage rating can be a limiting factor at high resistances.
If you intend to use Rx in high-voltage applications, you may need to choose a resistor with a higher voltage rating or consider adjusting your design to ensure safe operation.
Does this help, or is there something more specific you'd like to address about the resistor values?
1y

copilot

Given the power net voltage is 1000 VDC, the voltage across Rx will likely exceed the standard voltage rating for most SMD resistors, such as those in an 0603 package.
For a 100MΩ resistor like Rx in a circuit with 1000 VDC:
  • Electric Strength: Standard 0603 SMD resistors typically have a voltage rating of around 50V to 100V, which would be inadequate for 1000 VDC.
  • Power Dissipation: The power dissipated by Rx can be calculated using the formula:
    P=V2RP = \frac{V^2}{R}
    Let's calculate the power dissipation with the given values:
    P=10002100×106P = \frac{1000^2}{100 \times 10^6}
    P=0.01 WP = 0.01 \text{ W}
The power dissipation itself (0.01 W or 10 mW) might not be a problem if your resistor's power rating is adequate, but the 1000 VDC far exceeds the voltage rating of typical SMD resistors.
Recommendations:
  1. Higher Voltage Rating: Choose a resistor specifically designed for high-voltage applications. These are often physically larger and have higher voltage ratings.
  2. Series Configuration: Use multiple resistors in series to distribute the voltage across them if high voltage resistors aren't available.
  3. Check Datasheet: Always make sure to check the manufacturer's datasheet to confirm the component can handle your requirements.
Would you like help on how to implement these suggestions or anything else about your design?
1y
jetpace

jetpace

here powernet voltage is 1000 VDC
1y
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