×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Electrostatic Ground Shield

Electrostatic Ground Shield

Electrostatic Ground Shield

(OP)
Hi all,

My question is a bit wide, and I apologize for that.

Often, Electrostatic ground shield are used in Rectifier transformer, I manage to get the following explanation from :

Electric power transformer engineering / edited by James H. Harlow. // ISBN 0-8493-1704-5

Quote (Electric power transformer engineering):

"2.4.13 Electrostatic Ground Shield
It is usually desirable to have an electrostatic ground shield between the primary and secondary windings.
The electrostatic ground shield provides capacitive decoupling of the primary and secondary windings.
Generally, the winding connected to the rectifier circuit is ungrounded. Without the presence of the
electrostatic ground shield, transients on the primary side transfer to the secondary side of the transformer.
These may be approximately 50% of the magnitude of the primary transient if there are no
grounds in the system. This is high enough to fail secondary windings and core insulation or to cause
rectifier-circuit failures. The other normally considered advantage to the system is the minimization of
high-frequency disturbances to the primary system due to the rectifier second part
."

Ok for the second part about high-frequency disturbance from the rectifying process.

But I dont get why ungrounded secondaries systems are more vurnerable to disturbance (from primary) than grounded systems.

Could anyone clarify it for me?

Thank you in advance.

RE: Electrostatic Ground Shield

Because they have no reference to ground to keep the secondary voltage to ground at a known value.  Without the shield, transient overvoltages are capacitively coupled from the primary to the secondary.

RE: Electrostatic Ground Shield

Consider a 50 Volt circuit fed by a 500:50 Volt transformer.
If the secondary is grounded the maximum voltage will be 50 Volts to ground. The impedance of the transformer secondary will shunt most capacitively coupled transients. If the secondary is floating, then a high voltage transient on the primary may induce a high voltage to ground on the secondary circuit through capacitive coupling.
Basically what David said.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Electrostatic Ground Shield

(OP)
Ok, thanks for the explanation,

Ok, considering that transient overvoltage are mostly capacitive it makes sense.

One last question before I draw a equivalent scheme to fully grasp the concept.
So electromagnetic induced differential overvoltage is negligeable because it is shunt by the transformer?

Again thanks for the support.

RE: Electrostatic Ground Shield

"So electromagnetic induced differential overvoltage is negligeable because it is shunt by the transformer?"

Not quite. If the coupling mechanism is inductive which, after all, is the main coupling mechanism in a transformer, then it is mostly the stray inductance (the Xr of the transformer) that reduces coupled transients because of the high frequency components involved. The stray inductance is particularly effective if the secondary load is resistive or capacitive.

The electrostatic shield has no real influence on normal mode inductively coupled transients.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources