There is presently no way to protect the U.S. electrical grid (or any other electrical grid on earth) from an EMP or EMPS from any source

begin partial quote: 
But the best experience utilities have had in preparing for an EMP is tied to a natural phenomenon: solar flares.
While astronomers can see solar events, such as a coronal mass ejection, they don’t have a true picture of its magnitude until it’s about 90 minutes from Earth. The U.S. Space Weather Prediction Center will issue solar storm warnings in anticipation of these events. Grids are alerted to dangerous solar activity and geomagnetic storm watches are called. But with so little time to react, hardening networks ahead of time is more practical.

Transmission towers in Minooka, Illinois. The cost of protecting against an EMP strike could be in the billions of dollars.

Photographer: Daniel Acker

PJM Interconnection LLC, operator of the power grid serving one-fifth of America's population, has a lot of experience protecting systems against solar activity. PJM has also been working with transmission owners to protect against other threats, many of which have two specific characteristics: low probability and high potential for catastrophe, said Mike Bryson, vice president of operations for the Valley Forge, Pennsylvania-based operator. An EMP is one of them.
Power companies have made a few moves to protect against electromagnetic interference. Some grid operators and transmission infrastructure owners are putting in place so-called Faraday enclosures, shields of conductive material used to protect electronic equipment and facilities. Utilities have also started stockpiling spare parts to replace any that are damaged by an EMP event, storms or other disasters.
“I don’t think we have an illusion we will prevent it,” Bryson said in an interview. “That’s really the government’s job.”


end partial quote.

Though there are many types of EMPs

Solar Flare
local EMP
(Also every nuclear blast generate an EMP by the way.
 A Nationwide EMP caused by a 100 megaton hydrogen bomb at the right altitude would take out 90% of the electrical things in the Continental  U.S. but not Hawaii, Puerto Rico, U.S. Virgin Islands and Alaska (in other words most electrical things might not ever work again anywhere without buying new electrical things from another country and installing them here that wasn't hit by that nuclear EMP.

For example, all computer hard drives would permanently fry (never to be recovered or read from again) if they were above 10 feet below the ground in an all out nuclear EMP.

So, it depends upon the yield whether you lose everything electrical or not in any given area.
Also, in a 100 mile high 100 megaton blast everyone within 12 feet of anything metal usually dies.
However, a car or plane is a natural faraday cage so as long as you were not getting into or out of the car at the moment the EMP hit. If your foot or one foot was touching the ground and one and the car that likely could be fatal if this is exactly what you were doing the moment this EMP hit either locally or nationwide in the Continental United States.

Note: When I was researching for writing EMP I went to a university site where Graduate students had studied all this in detail and had written either their Master's or PHd thesis on this subject.

end note:

So, I'm estimating about 70 million people would die the moment a 100 megaton Hydrogen bomb went off at 100 miles up from electrocution from being within 12 feet of anything metal (unless it was in a faraday cage like a car, truck or plane or maybe even a train. (not sure if a train is also a faraday cage).